Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download (some) Python for Crystallographers
Document related concepts
no text concepts found
Transcript
(some) Python for Crystallographers Fermin Otálora [email protected] Laboratorio de Estudios Cristalográficos IACT, CSIC / U. Granada CSDC / MCC M3-T09 Grenoble, Junio 2009 This presentation contains materials from a presentation by Eric Jones and Travis Oliphant. Original materials can be found at http://nanohub.org/resources/99. FORmula TRANslation A B C C++ Monty Python Flying Circus What is Python ten years ago. . . Python in Crystallography F. Otálora Introduction What is Python Comparisons In 1999, Van Rossum submitted a funding proposal to DARPA called “Computer Programming for Everybody”, in which he further defined his goals for Python: The Language Numbers Strings Lists Dictionaries Tuples • an easy and intuitive language just as powerful Assignment as major competitors Control Structures Functions • open source, so anyone can contribute to its Modules development Classes Misc • code that is as understandable as plain English ndarrays • suitability for everyday tasks, allowing for short development times Guido van Rossum What’s Python? Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • A interpreted, very high level, general purpose, portable languaje with a focus on productivity via modularity, uniformity, simplicity, pragmatism • • • • clean, spare syntax simple, regular, powerful semantics object oriented, multiparadigm easy modularity • A rich standard library of modules • A strong Open Source community • Python Software Foundation • many users (individuals and companies) • lots of 3rd-party tools/add-ons • sub-communities for special interests • Several good implementations (CPython, PyPy, IronPython, Jython) • Excellet for scripting, rapid prototyping and glueing external libraries and applications • Less lines to read makes code faster to write, less error prone and easier to understand, maintain and debug • A reduced number of keywords with only one meaning consistently used in different contexts • Syntax enforces structure and documentation What’s Python? Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • A interpreted, very high level, general purpose, portable languaje with a focus on productivity via modularity, uniformity, simplicity, pragmatism • • • • clean, spare syntax simple, regular, powerful semantics object oriented, multiparadigm easy modularity • A rich standard library of modules • A strong Open Source community • Python Software Foundation • many users (individuals and companies) • lots of 3rd-party tools/add-ons • sub-communities for special interests • Several good implementations (CPython, PyPy, IronPython, Jython) • Excellet for scripting, rapid prototyping and glueing external libraries and applications • “Batteries Included” • Second largest after Java What’s Python? Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • A interpreted, very high level, general purpose, portable languaje with a focus on productivity via modularity, uniformity, simplicity, pragmatism • • • • clean, spare syntax simple, regular, powerful semantics object oriented, multiparadigm easy modularity • A rich standard library of modules • A strong Open Source community • Python Software Foundation • many users (individuals and companies) • lots of 3rd-party tools/add-ons • sub-communities for special interests • Several good implementations (CPython, PyPy, IronPython, Jython) • Excellet for scripting, rapid prototyping and glueing external libraries and applications What’s Python? Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • A interpreted, very high level, general purpose, portable languaje with a focus on productivity via modularity, uniformity, simplicity, pragmatism • • • • clean, spare syntax simple, regular, powerful semantics object oriented, multiparadigm easy modularity • A rich standard library of modules • A strong Open Source community • Python Software Foundation • many users (individuals and companies) • lots of 3rd-party tools/add-ons • sub-communities for special interests • Several good implementations (CPython, PyPy, IronPython, Jython) • Excellet for scripting, rapid prototyping and glueing external libraries and applications CPython http://www.python.org/ PyPy http://codespeak.net/pypy/dist/pypy/doc/ Jython http://www.jython.org/ IronPython http://www.codeplex.com/Wiki/View.aspx?ProjectName=IronPy What’s Python? Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • A interpreted, very high level, general purpose, portable languaje with a focus on productivity via modularity, uniformity, simplicity, pragmatism • • • • clean, spare syntax simple, regular, powerful semantics object oriented, multiparadigm easy modularity • A rich standard library of modules • A strong Open Source community • Python Software Foundation • many users (individuals and companies) • lots of 3rd-party tools/add-ons • sub-communities for special interests • Several good implementations (CPython, PyPy, IronPython, Jython) • Excellet for scripting, rapid prototyping and glueing external libraries and applications Bubblesort (Pseudocode) Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays function bubblesort (A : l i s t [ 1 . . n ] ) var i n t i , j ; f o r i from n downto 1 f o r j from 1 to i −1 i f (A[ j ] > A[ j +1]) swap (A[ j ] , A[ j +1]) Bubblesort (C) Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays void bubbleSort ( i n t ∗ array , i n t length ) { i n t i , j , temp ; int test ; f o r ( i = length − 1; i > 0; i −−) { t e s t =0; f o r ( j = 0; j < i ; j ++) { i f ( array [ j ] > array [ j +1]) { temp = array [ j ] ; array [ j ] = array [ j +1]; array [ j +1] = temp ; t e s t =1; } } i f ( t e s t ==0) break ; } } Bubblesort (Java) Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays public s t a t i c void bubbleSort ( i n t [ ] data ) { f o r ( i n t k = 0; k < data . length − 1; k++) { boolean isSorted = true ; f o r ( i n t i = 1; i < data . length − k ; i ++) { i f ( data [ i ] < data [ i − 1 ] ) { i n t tempVariable = data [ i ] ; data [ i ] = data [ i − 1 ] ; data [ i − 1] = tempVariable ; isSorted = f a l s e ; } } i f ( isSorted ) break ; } } Bubblesort (Fortran 1/2) Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays SUBROUTINE sort ( array_x , array_y , datasize ) REAL array_x ( ∗ ) REAL array_y ( ∗ ) INTEGER datasize REAL x_temp REAL y_temp LOGICAL inorder inorder = . f a l s e . do 90 while ( inorder . eq . . f a l s e . ) inorder = . true . do 91 i =1, datasize i f ( array_x ( i ) . eq . array_x ( i +1) ) then i f ( array_y ( i ) . l t . array_y ( i +1) ) then x_temp = array_x ( i ) y_temp = array_y ( i ) array_x ( i ) = array_x ( i +1) array_y ( i ) = array_y ( i +1) array_x ( i +1) = x_temp array_y ( i +1) = y_temp inorder = . f a l s e . endif endif Bubblesort (Fortran 2/2) Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays 91 90 i f ( array_x ( i ) . l t . array_x ( i +1) ) then x_temp = array_x ( i ) y_temp = array_y ( i ) array_x ( i ) = array_x ( i +1) array_y ( i ) = array_y ( i +1) array_x ( i +1) = x_temp array_y ( i +1) = y_temp inorder = . f a l s e . endif continue continue END SUBROUTINE sort Bubblesort (Pseudocode, Python) Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists function bubblesort (A : l i s t [ 1 . . n ] ) var i n t i , j ; f o r i from n downto 1 f o r j from 1 to i −1 i f (A[ j ] > A[ j +1]) swap (A[ j ] , A[ j +1]) Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays def bubblesort ( l ) : f o r passesLeft in range ( len ( l )−1, 0 , −1): f o r index in range ( passesLeft ) : i f l [ index ] < l [ index + 1 ] : l [ index ] , l [ index + 1] = l [ index + 1 ] , l [ index ] return l Comparisons (Eficiency) Python in Crystallography FORTRAN C C++ Java F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays Perl Python is interpreted Execution in Python is slow Comparisons (Eficiency) Python in Crystallography FORTRAN C C++ Java F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays Perl Python is interpreted Execution in Python is slow, but mumber crunching is done in C or FORTRAN anyway via extension libraries Comparisons (Eficiency) Python in Crystallography FORTRAN C C++ Java F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays Perl Python is “Programmer-Oriented” Execution in Python is slow, but mumber crunching is done in C or FORTRAN anyway via extension libraries and development, debuging and maintenance are very eficient and easy in Python. Comparison (Programming paradigm) Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • FORTRAN • Application, scientific and engineering • Imperative, procedural, object-oriented • Medium/High (Compiler “extensions”) • Medium • Small • C / C++ • System / Application, System • Imperative / Imperative, object-oriented, generic • Very high / Very high • Medium / High • Medium / Large • Python • Application, Scripting, Prototyping, Web • Imperative, object-oriented, functional, aspect-oriented, reflective • Almost complete • Small • Very Large • Java • Application, Web • Imperative, procedural, reflective, functional, object-oriented, generic • Complete • Medium • Huge • Perl • Application, Text processing, Scripting, Web • Imperative, object-oriented, functional, reflective • Almost complete • High • Large Comparison (Portability) Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • FORTRAN • Application, scientific and engineering • Imperative, procedural, object-oriented • Medium/High (Compiler “extensions”) • Medium • Small • C / C++ • System / Application, System • Imperative / Imperative, object-oriented, generic • Very high / Very high • Medium / High • Medium / Large • Python • Application, Scripting, Prototyping, Web • Imperative, object-oriented, functional, aspect-oriented, reflective • Almost complete • Small • Very Large • Java • Application, Web • Imperative, procedural, reflective, functional, object-oriented, generic • Complete • Medium • Huge • Perl • Application, Text processing, Scripting, Web • Imperative, object-oriented, functional, reflective • Almost complete • High • Large Comparison (Complexity) Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • FORTRAN • Application, scientific and engineering • Imperative, procedural, object-oriented • Medium/High (Compiler “extensions”) • Medium • Small • C / C++ • System / Application, System • Imperative / Imperative, object-oriented, generic • Very high / Very high • Medium / High • Medium / Large • Python • Application, Scripting, Prototyping, Web • Imperative, object-oriented, functional, aspect-oriented, reflective • Almost complete • Small • Very Large • Java • Application, Web • Imperative, procedural, reflective, functional, object-oriented, generic • Complete • Medium • Huge • Perl • Application, Text processing, Scripting, Web • Imperative, object-oriented, functional, reflective • Almost complete • High • Large Comparison (Standard Library) Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • FORTRAN • Application, scientific and engineering • Imperative, procedural, object-oriented • Medium/High (Compiler “extensions”) • Medium • Small • C / C++ • System / Application, System • Imperative / Imperative, object-oriented, generic • Very high / Very high • Medium / High • Medium / Large • Python • Application, Scripting, Prototyping, Web • Imperative, object-oriented, functional, aspect-oriented, reflective • Almost complete • Small • Very Large • Java • Application, Web • Imperative, procedural, reflective, functional, object-oriented, generic • Complete • Medium • Huge • Perl • Application, Text processing, Scripting, Web • Imperative, object-oriented, functional, reflective • Almost complete • High • Large Comparison (Field of application) Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • FORTRAN • Application, scientific and engineering • Imperative, procedural, object-oriented • Medium/High (Compiler “extensions”) • Medium • Small • C / C++ • System / Application, System • Imperative / Imperative, object-oriented, generic • Very high / Very high • Medium / High • Medium / Large • Python • Application, Scripting, Prototyping, Web • Imperative, object-oriented, functional, aspect-oriented, reflective • Almost complete • Small • Very Large • Java • Application, Web • Imperative, procedural, reflective, functional, object-oriented, generic • Complete • Medium • Huge • Perl • Application, Text processing, Scripting, Web • Imperative, object-oriented, functional, reflective • Almost complete • High • Large Using Python Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • Interactive interpreter • Souce files (autocompilation) • Interpreter + Editor • Especialized editor or IDEs Using Python Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • Interactive interpreter • Souce files (autocompilation) • Interpreter + Editor • Especialized editor or IDEs Using Python Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • Interactive interpreter • Souce files (autocompilation) • Interpreter + Editor • Especialized editor or IDEs Using Python Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • Interactive interpreter • Souce files (autocompilation) • Interpreter + Editor • Especialized editor or IDEs Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays The Language Interactive Calculator Python in Crystallography enthought ® Interactive Calculator F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays # adding two values >>> 1 + 1 2 # setting a variable >>> a = 1 >>> a 1 # checking a variables type >>> type(a) <type 'int'> # an arbitrarily long integer >>> a = 1203405503201 >>> a 1203405503201L >>> type(a) <type 'long'> # real numbers >>> b = 1.2 + 3.1 >>> b 4.2999999999999998 >>> type(b) <type 'float'> # complex numbers >>> c = 2+1.5j >>> c (2+1.5j) The four numeric types in Python on 32-bit architectures are: integer (4 byte) long integer (any precision) float (8 byte like C’s double) complex (16 byte) The Numeric module, which we will see later, supports a larger number of numeric types. Strings Python in Crystallography enthought ® Strings F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays CREATING STRINGS STRING LENGTH # using double quotes >>> s = “hello world” >>> print s hello world # single quotes also work >>> s = ‘hello world’ >>> print s hello world >>> s = “12345” >>> len(s) 5 STRING OPERATIONS # concatenating two strings >>> “hello “ + “world” ‘hello world’ # repeating a string >>> “hello “ * 3 ‘hello hello hello ’ FORMAT STRINGS # the % operator allows you # to supply values to a # format string. The format # string follows # C conventions. >>> s = “some numbers:” >>> x = 1.34 >>> y = 2 >>> s = “%s %f, %d” % (s,x,y) >>> print s some numbers: 1.34, 2 The string module Python in Crystallography enthought ® The string module F. Otálora Introduction >>> import string >>> s = “hello world” What is Python Comparisons The Language Numbers Strings Lists # split space delimited words >>> wrd_lst = string.split(s) >>> print wrd_lst [‘hello’, ‘world’] Dictionaries Tuples Assignment Control Structures Functions # python2.2 and higher >>> s.split() [‘hello’, ‘world’] Modules Classes Misc ndarrays # join words back together >>> string.join(wrd_lst) hello world # python2.2 and higher >>> ‘ ‘.join(wrd_lst) hello world # replacing text in a string >>> string.replace(s,’world’ \ ... ,’Mars’) ‘hello Mars’ # python2.2 and higher >>> s.replace(’world’ ,’Mars’) ‘hello Mars’ # strip whitespace from string >>> s = “\t hello \n” >>> string.strip(s) ‘hello’ # python2.2 and higher >>> s.strip() ‘hello’ Multiline strings Python in Crystallography Multi-line Strings F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples # triple quotes are used # for mutli-line strings >>> a = ”””hello ... world””” >>> print a hello world Assignment Control Structures Functions Modules Classes Misc ndarrays # multi-line strings using # “\” to indicate continuation >>> a = “hello ” \ ... “world” >>> print a hello world # including the new line >>> a = “hello\n” \ ... “world” >>> print a hello world enthought ® List Objects Python in Crystallography enthought ® List objects F. Otálora Introduction What is Python Comparisons The Language LIST CREATION WITH BRACKETS range( start, stop, step) >>> l = [10,11,12,13,14] >>> print l [10, 11, 12, 13, 14] # the range method is helpful # for creating a sequence >>> range(5) [0, 1, 2, 3, 4] Numbers Strings Lists Dictionaries Tuples Assignment Control Structures CONCATENATING LIST # simply use the + operator >>> [10, 11] + [12,13] [10, 11, 12, 13] Functions Modules Classes Misc ndarrays REPEATING ELEMENTS IN LISTS # the multiply operator # does the trick. >>> [10, 11] * 3 [10, 11, 10, 11, 10, 11] >>> range(2,7) [2, 3, 4, 5, 6] >>> range(2,7,2) [2, 4, 6] Indexing Python in Crystallography enthought ® Indexing F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists RETREIVING AN ELEMENT NEGATIVE INDICES # list # indices: 0 1 2 3 4 >>> l = [10,11,12,13,14] >>> l[0] 10 # # # # # Dictionaries Tuples Assignment Control Structures Functions Modules SETTING AN ELEMENT >>> l[1] = 21 >>> print l [10, 21, 12, 13, 14] Classes Misc negative indices count backward from the end of the list. indices: -5 -4 -3 -2 -1 >>> l = [10,11,12,13,14] >>> l[-1] 14 >>> l[-2] 13 OUT OF BOUNDS ndarrays >>> l[10] Traceback (innermost last): File "<interactive input>",line 1,in ? IndexError: list index out of range The first element in an array has index=0 as in C. Take note Fortran programmers! More on lists Python in Crystallography enthought ® More on list objects F. Otálora Introduction What is Python LIST CONTAINING MULTIPLE TYPES Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures # list containing integer, # string, and another list. >>> l = [10,’eleven’,[12,13]] >>> l[1] ‘eleven’ >>> l[2] [12, 13] Functions Modules Classes Misc ndarrays # use multiple indices to # retrieve elements from # nested lists. >>> l[2][0] 12 LENGTH OF A LIST >>> len(l) 3 DELETING OBJECT FROM LIST # use the del keyword >>> del l[2] >>> l [10,’eleven’] DOES THE LIST CONTAIN x ? # use in or not in >>> l = [10,11,12,13,14] >>> 13 in l 1 >>> 13 not in l 0 Slicing Python in Crystallography enthought ® Slicing F. Otálora var[lower:upper] Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays Slices extract a portion of a sequence by specifying a lower and upper bound. The extracted elements start at lower and go up to, but do not include, the upper element. Mathematically the range is [lower,upper). SLICING LISTS OMITTING INDICES # indices: 0 1 2 3 4 >>> l = [10,11,12,13,14] # [10,11,12,13,14] >>> l[1:3] [11, 12] # omitted boundaries are # assumed to be the beginning # (or end) of the list. # negative indices work also >>> l[1:-2] [11, 12] >>> l[-4:3] [11, 12] # grab first three elements >>> l[:3] [10,11,12] # grab last two elements >>> l[-2:] [13,14] A few methods for list objects Python in Crystallography enthought ® A few methods for list objects F. Otálora Introduction What is Python Comparisons The Language Numbers some_list.append( x ) some_list.remove( x ) Add the element x to the end of the list, some_list. Delete the first occurrence of x from the list. some_list.count( x ) some_list.reverse( ) Count the number of times x occurs in the list. Reverse the order of elements in the list. some_list.index( x ) some_list.sort( cmp ) Return the index of the first occurrence of x in the list. By default, sort the elements in ascending order. If a compare function is given, use it to sort the list. Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays List methods in action Python in Crystallography List methods in action F. Otálora Introduction >>> l = [10,21,23,11,24] What is Python Comparisons The Language Numbers Strings Lists # add an element to the list >>> l.append(11) >>> print l [10,21,23,11,24,11] # remove the first 11 >>> l.remove(11) >>> print l [10,21,23,24,11] # how many 11s are there? >>> l.count(11) 2 # sort the list >>> l.sort() >>> print l [10,11,21,23,24] # where does 11 first occur? >>> l.index(11) 3 # reverse the list >>> l.reverse() >>> print l [24,23,21,11,10] Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays enthought ® Mutable vs. Inmutable Python in Crystallography enthought ® Mutable vs. Immutable F. Otálora Introduction What is Python Comparisons The Language Numbers Strings MUTABLE OBJECTS IMMUTABLE OBJECTS # Mutable objects, such as # lists, can be changed # in-place. # Immutable objects, such as # strings, cannot be changed # in-place. # insert new values into list >>> l = [10,11,12,13,14] >>> l[1:3] = [5,6] >>> print l [10, 5, 6, 13, 14] # try inserting values into # a string >>> s = ‘abcde’ >>> s[1:3] = ‘xy’ Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays The cStringIO module treats strings like a file buffer and allows insertions. It’s useful when working with large strings or when speed is paramount. Traceback (innermost last): File "<interactive input>",line 1,in ? TypeError: object doesn't support slice assignment # here’s how to do it >>> s = s[:1] + ‘xy’ + s[3:] >>> print s 'axyde' Dictionaries Python in Crystallography enthought ® Dictionaries F. Otálora Introduction What is Python Comparisons The Language Dictionaries store key/value pairs. Indexing a dictionary by a key returns the value associated with it. DICTIONARY EXAMPLE Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays # create an empty dictionary using curly brackets >>> record = {} >>> record[‘first’] = ‘Jmes’ >>> record[‘last’] = ‘Maxwell’ >>> record[‘born’] = 1831 >>> print record {'first': 'Jmes', 'born': 1831, 'last': 'Maxwell'} # create another dictionary with initial entries >>> new_record = {‘first’: ‘James’, ‘middle’:‘Clerk’} # now update the first dictionary with values from the new one >>> record.update(new_record) >>> print record {'first': 'James', 'middle': 'Clerk', 'last':'Maxwell', 'born': 1831} A few dictionary methods enthought ® Python in Crystallography F. Otálora A few dictionary methods Introduction What is Python some_dict.clear( ) some_dict.keys( ) Remove all key/value pairs from the dictionary, some_dict. Return a list of all the keys in the dictionary. some_dict.copy( ) some_dict.values( ) Create a copy of the dictionary Return a list of all the values in the dictionary. some_dict.has_key( x ) some_dict.items( ) Test whether the dictionary contains the key x. Return a list of all the key/value pairs in the dictionary. Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays Dictionary methods in action Python in Crystallography enthought ® Dictionary methods in action F. Otálora Introduction What is Python >>> d = {‘cows’: 1,’dogs’:5, ... ‘cats’: 3} Comparisons The Language Numbers Strings Lists Dictionaries # create a copy. >>> dd = d.copy() >>> print dd {'dogs':5,'cats':3,'cows': 1} # get a list of all values >>> d.values() [3, 5, 1] # test for chickens. >>> d.has_key(‘chickens’) 0 # return the key/value pairs >>> d.items() [('cats', 3), ('dogs', 5), ('cows', 1)] # get a list of all keys >>> d.keys() [‘cats’,’dogs’,’cows’] # clear the dictionary >>> d.clear() >>> print d {} Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays Tuples Python in Crystallography enthought ® Tuples F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays Tuples are a sequence of objects just like lists. Unlike lists, tuples are immutable objects. While there are some functions and statements that require tuples, they are rare. A good rule of thumb is to use lists whenever you need a generic sequence. TUPLE EXAMPLE # tuples are built from a comma separated list enclosed by ( ) >>> t = (1,’two’) >>> print t (1,‘two’) >>> t[0] 1 # assignments to tuples fail >>> t[0] = 2 Traceback (innermost last): File "<interactive input>", line 1, in ? TypeError: object doesn't support item assignment Assignment Python in Crystallography enthought ® Assignment F. Otálora Introduction What is Python Assignment creates object references. Comparisons The Language Numbers Strings >>> x = [0, 1, 2] x # y = x cause x and y to point # at the same list >>> y = x y 0 1 2 Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays # changes to y also change x >>> y[1] = 6 >>> print x [0, 6, 2] x # re-assigning y to a new list # decouples the two lists >>> y = [3, 4] x 0 6 2 y 3 4 y 0 6 2 Multiple Assignment Python in Crystallography enthought ® Multiple assignments F. Otálora Introduction What is Python Comparisons The Language # creating a tuple without () >>> d = 1,2,3 >>> d (1, 2, 3) Numbers # multiple assignments from a # tuple >>> a,b,c = d >>> print b 2 Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays # multiple assignments >>> a,b,c = 1,2,3 >>> print b 2 # also works for lists >>> a,b,c = [1,2,3] >>> print b 2 If statements Python in Crystallography enthought ® If statements F. Otálora Introduction What is Python Comparisons The Language if/elif/else provide conditional execution of code blocks. Numbers Strings Lists Dictionaries Tuples IF STATEMENT FORMAT Assignment Control Structures Functions Modules Classes Misc ndarrays if <condition>: <statements> elif <condition>: <statements> else: <statements> IF EXAMPLE # a >>> >>> ... ... ... ... ... ... 1 simple if statement x = 10 if x > 0: print 1 elif x == 0: print 0 else: print –1 < hit return > Test values Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Test Values • True means any non-zero number or non-empty object • False means not true: zero, empty object, or None Assignment Control Structures EMPTY OBJECTS Functions Modules Classes Misc ndarrays # empty objects evaluate false >>> x = [] >>> if x: ... print 1 ... else: ... print 0 ... < hit return > 0 enthought ® For Loops Python in Crystallography F. Otálora Introduction enthought ® For loops For loops iterate over a sequence of objects. What is Python Comparisons The Language Numbers for <loop_var> in <sequence>: <statements> Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes TYPICAL SCENARIO LOOPING OVER A LIST >>> for i in range(5): ... print i, ... < hit return > 0 1 2 3 4 >>> l=[‘dogs’,’cats’,’bears’] >>> accum = ‘’ >>> for item in l: ... accum = accum + item ... accum = accum + ‘ ‘ ... < hit return > >>> print accum dogs cats bears Misc ndarrays LOOPING OVER A STRING >>> for i in ‘abcde’: ... print i, ... < hit return > a b c d e While loops Python in Crystallography enthought ® While loops F. Otálora Introduction While loops iterate until a condition is met. What is Python Comparisons while <condition>: <statements> The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays WHILE LOOP BREAKING OUT OF A LOOP # the condition tested is # whether lst is empty. >>> lst = range(3) >>> while lst: ... print lst ... lst = lst[1:] ... < hit return > [0, 1, 2] [1, 2] [2] # breaking from an infinite # loop. >>> i = 0 >>> while 1: ... if i < 3: ... print i, ... else: ... break ... i = i + 1 ... < hit return > 0 1 2 Anatomy of a function Python in Crystallography enthought ® Anatomy of a function F. Otálora Introduction What is Python Comparisons The keyword def indicates the start of a function. Function arguments are listed separated by commas. They are passed by assignment. More on this later. The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays Indentation is used to indicate the contents of the function. It is not optional, but a part of the syntax. def add(arg0, arg1): a = arg0 + arg1 return a A colon ( : ) terminates the function definition. An optional return statement specifies the value returned from the function. If return is omitted, the function returns the special value None. Parameters can be positional or keyworded and can be optional with default values. Our new function in action Python in Crystallography enthought ® Our new function in action F. Otálora Introduction What is Python Comparisons The Language Numbers Strings # We’ll create our function # on the fly in the # interpreter. >>> def add(x,y): ... a = x + y ... return a # how about strings? >>> x = ‘foo’ >>> y = ‘bar’ >>> add(x,y) ‘foobar’ # test it out with numbers >>> x = 2 >>> y = 3 >>> add(x,y) 5 # functions can be assigned # to variables >>> func = add >>> func(x,y) ‘foobar’ Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays # how about numbers and strings? >>> add(‘abc',1) Traceback (innermost last): File "<interactive input>", line 1, in ? File "<interactive input>", line 2, in add TypeError: cannot add type "int" to string Modules Python in Crystallography enthought ® Modules F. Otálora Introduction What is Python Comparisons The Language Numbers EX1.PY FROM SHELL # ex1.py [ej@bull ej]$ python ex1.py 6, 3.1416 PI = 3.1416 FROM INTERPRETER def sum(lst): tot = lst[0] for value in lst[1:]: tot = tot + value return tot # load and execute the module >>> import ex1 6, 3.1416 # get/set a module variable. >>> ex1.PI 3.1415999999999999 >>> ex1.PI = 3.14159 >>> ex1.PI 3.1415899999999999 # call a module variable. >>> t = [2,3,4] >>> ex1.sum(t) 9 Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays l = [0,1,2,3] print sum(l), PI Modules Python in Crystallography enthought ® Modules cont. F. Otálora Introduction INTERPRETER EDITED EX1.PY # load and execute the module >>> import ex1 6, 3.1416 < edit file > # import module again >>> import ex1 # nothing happens!!! # ex1.py version 2 What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays # use reload to force a # previously imported library # to be reloaded. >>> reload(ex1) 10, 3.14159 PI = 3.14159 def sum(lst): tot = 0 for value in lst: tot = tot + value return tot l = [0,1,2,3,4] print sum(l), PI Modules Python in Crystallography enthought ® Modules cont. 2 F. Otálora Introduction Modules can be executable scripts or libraries or both. What is Python Comparisons The Language Numbers EX2.PY EX2.PY CONTINUED “ An example module “ def add(x,y): ” Add two values.” a = x + y return a Strings Lists Dictionaries PI = 3.1416 Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays def sum(lst): ””” Sum the values in a list. ””” tot = 0 for value in lst: tot = tot + value return tot def test(): l = [0,1,2,3] assert( sum(l) == 6) print ‘test passed’ # this code runs only if this # module is the main program if __name__ == ‘__main__’: test() Setting up PYTHONPATH Python in Crystallography enthought ® Setting up PYTHONPATH F. Otálora Introduction What is Python PYTHONPATH is an environment variable (or set of registry entries on Windows) that lists the directories Python searches for modules. Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment WINDOWS The easiest way to set the search paths is using PythonWin’s Tools->Edit Python Path menu item. Restart PythonWin after changing to insure changes take affect. UNIX -- .cshrc !! note: the following should !! !! all be on one line !! setenv PYTHONPATH $PYTHONPATH:$HOME/aces Control Structures Functions Modules Classes Misc ndarrays UNIX -- .bashrc PYTHONPATH=$PYTHONPATH:$HOME/aces export PYTHONPATH Classes Python in Crystallography enthought ® Classes F. Otálora SIMPLE PARTICLE CLASS Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays >>> class particle: ... # Constructor method ... def __init__(self,mass, velocity): ... # assign attribute values of new object ... self.mass = mass ... self.velocity = velocity ... # method for calculating object momentum ... def momentum(self): ... return self.mass * self.velocity ... # a “magic” method defines object’s string representation ... def __repr__(self): ... msg = "(m:%2.1f, v:%2.1f)" % (self.mass,self.velocity) ... return msg EXAMPLE >>> a = particle(3.2,4.1) >>> a (m:3.2, v:4.1) >>> a.momentum() 13.119999999999999 Reading files Python in Crystallography enthought ® Reading files F. Otálora Introduction FILE INPUT EXAMPLE PRINTING THE RESULTS >>> results = [] >>> f = open(‘c:\\rcs.txt’,’r’) >>> for i in results: print i [100.0, -20.30…, -31.20…] [200.0, -22.70…, -33.60…] What is Python Comparisons The Language Numbers Strings Lists Dictionaries # read lines and discard header >>> lines = f.readlines()[1:] >>> f.close() Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays >>> for l in lines: ... # split line into fields ... fields = line.split() ... # convert text to numbers ... freq = float(fields[0]) ... vv = float(fields[1]) ... hh = float(fields[2]) ... # group & append to results ... all = [freq,vv,hh] ... results.append(all) ... < hit return > EXAMPLE FILE: RCS.TXT #freq (MHz) vv (dB) hh (dB) 100 -20.3 -31.2 200 -22.7 -33.6 More compact version Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc More compact version ITERATING ON A FILE AND LIST COMPREHENSIONS >>> results = [] >>> f = open(‘c:\\rcs.txt’,’r’) >>> f.readline() ‘#freq (MHz) vv (dB) hh (dB)\n' >>> for l in f: ... all = [float(val) for val in l.split()] ... results.append(all) ... < hit return > >>> for i in results: ... print i ... < hit return > ndarrays EXAMPLE FILE: RCS.TXT #freq (MHz) 100 200 vv (dB) -20.3 -22.7 hh (dB) -31.2 -33.6 enthought ® One line Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Same thing, one line OBFUSCATED PYTHON CONTEST… >>> print [[float(val) for val in l.split()] for ... l in open("c:\\temp\\rcs.txt","r") ... if l[0] !="#"] Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays EXAMPLE FILE: RCS.TXT #freq (MHz) 100 200 vv (dB) -20.3 -22.7 hh (dB) -31.2 -33.6 enthought ® Data persistency enthought ® Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Pickling and Shelves Pickling is Python’s term for persistence. Pickling can write arbitrarily complex objects to a file. The object can be resurrected from the file at a later time for use in a program. Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays >>> import shelve >>> f = shelve.open(‘c:/temp/pickle’,’w’) >>> import ex_material >>> epoxy_gls = ex_material.constant_material(4.8,1) >>> f[‘epoxy_glass’] = epoxy_gls >>> f.close() < kill interpreter and restart! > >>> import shelve >>> f = shelve.open(‘c:/temp/pickle’,’r’) >>> epoxy_glass = f[‘epoxy_glass’] >>> epoxy_glass.eps(100e6) 4.249e-11 Exception handling Python in Crystallography enthought ® Exception Handling F. Otálora ERROR ON LOG OF ZERO Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays import math >>> math.log10(10.) 1. >>> math.log10(0.) Traceback (innermost last): OverflowError: math range error CATCHING ERROR AND CONTINUING >>> a = 0. >>> try: ... r = math.log10(a) ... except OverflowError: ... print ‘Warning: overflow occurred. Value set to 0.’ ... # set value to 0. and continue ... r = 0. Warning: overflow occurred. Value set to 0. >>> print r 0.0 Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays ndarray (numpy) NumPy Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language • NumPy’s main object is the homogeneous multidimensional array (ndarray). This is a table of elements (usually numbers), all of the same type, indexed by a tuple of positive integers. Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays >>> from numpy import ∗ # create an array out of a l i s t >>> a = array ( [ 10, 20, 30, 40 ] ) >>> a array ( [ 1 0 , 20, 30, 40]) # create an array of 4 integers , from 0 to 3 >>> b = arange ( 4 ) >>> b array ( [ 0 , 1 , 2 , 3 ] ) # create an array of 3 evenly spaced samples from −pi to pi >>> c = linspace (−pi , pi , 3 ) >>> c array ([−3.14159265, 0. , 3.14159265]) Python in Crystallography Multidimensional arrays. Placeholder constructors F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays # A sequence of sequences produces a bidimensional array >>> b = array ( [ ( 1 . 5 , 2 , 3 ) , ( 4 , 5 , 6 ) ] ) >>> b array ( [ [ 1.5 , 2. , 3. ] , [ 4. , 5. , 6. ] ] ) # The shape can be s p e c i f i e d upon creation >>> zeros ( ( 3 , 4 ) ) array ( [ [ 0 . , 0 . , 0 . , 0 . ] , [0. , 0. , 0. , 0.] , [0. , 0. , 0. , 0 . ] ] ) # the type can also be s p e c i f i e d >>> ones ( ( 2 , 3 , 4 ) , dtype=int16 ) array ( [ [ [ 1 , 1 , 1 , 1 ] , [ 1, 1, 1, 1] , [ 1, 1, 1, 1]] , [ [ 1, 1, 1, 1] , [ 1, 1, 1, 1] , [ 1 , 1 , 1 , 1 ] ] ] , dtype=int16 ) # L e f t values unspecified >>> empty ( ( 2 , 3 ) ) array ( [ [ 3.73603959e−262, 6.02658058e−154, 6.55490914e−260], [ 5.30498948e−313, 3.14673309e−307, 1.00000000e +000]]) ndarray objects Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language >>> a = arange ( 1 0 ) . reshape ( 2 , 5 ) >>> a array ( [ [ 0 , 1 , 2 , 3 , 4 ] , [5 , 6, 7, 8, 9 ] ] ) >>> type ( a ) <type ’numpy. ndarray ’> Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays a.ndim 2 the number of axes (dimensions) of the array a.shape (2,5) the dimensions of the array (a tuple of integers indicating the size of the array in each dimension) a.size 10 the total number of elements of the array (product of the elements of shape) a.dtype int32 an object describing the type of the elements in the array (bool_, character, int_, int8, int16, int32, int64, float_, float8, float16, float32, float64, complex_, complex64, object_) a.itemsize 4 the size in bytes of each element of the array (equivalent to ndarray.dtype.itemsize) a.data the buffer containing the actual elements of the array (seldomly used) Ranges Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays >>> arange ( 10, 30, 5 ) array ( [ 1 0 , 15, 20, 25]) # i t accepts f l o a t arguments >>> arange ( 0 , 2 , 0.3 ) array ( [ 0. , 0.3 , 0.6 , 0.9 , 1.2 , 1.5 , 1 . 8 ] ) # 9 numbers from 0 to 2 >>> linspace ( 0 , 2 , 9 ) array ( [ 0. , 0.25 , 0.5 , 0.75 , 1. , 1.25 , 1.5 , # useful to evaluate function at l o t s of points >>> x = linspace ( 0 , 2∗ pi , 100 ) 1.75 , 2. ]) Element-wise operations Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays >>> a = array ( [20 ,30 ,40 ,50] ) >>> b = arange ( 4 ) >>> c = a−b >>> c array ( [ 2 0 , 29, 38, 47]) >>> b∗∗2 array ( [ 0 , 1 , 4 , 9 ] ) >>> 10∗ sin ( a ) array ( [ 9.12945251, −9.88031624, 7.4511316 , −2.62374854]) >>> a<35 array ( [ True , True , False , False ] , dtype=bool ) Common pitfall: Multiplication is also elementwise. Matrix product can be performed using the dot function or creating matrix objects. In-place operations Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • It is possible to perform some operations inplace so that no new array is created. >>> a = ones ( ( 2 , 3 ) , dtype= i n t ) >>> b = random . random ( ( 2 , 3 ) ) >>> a ∗= 3 >>> a array ( [ [ 3 , 3 , 3 ] , [3 , 3, 3 ] ] ) >>> b += a >>> b array ( [ [ 3.69092703, 3.8324276 , [ 3.18679111, 3.3039349 , # b i s converted to integer type >>> a += b >>> a array ( [ [ 6 , 6 , 6 ] , [6 , 6, 6 ] ] ) 3.0114541 ] , 3.37600289]]) Mixed-type operations Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • When operating with arrays of different types, the type of the resulting array corresponds to the more general or precise one. >>> a = ones ( 3 , dtype=int32 ) >>> b = linspace ( 0 , pi , 3 ) >>> b . dtype .name ’ float64 ’ >>> c = a+b >>> c array ( [ 1. , 2.57079633, 4.14159265]) >>> c . dtype .name ’ float64 ’ >>> d = exp ( c ∗1 j ) >>> d array ( [ 0.54030231+0.84147098j , −0.84147098+0.54030231j , −0.54030231−0.84147098 j ] ) >>> d . dtype .name ’complex128 ’ Unary operator methods Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays >>> a = random . random ( ( 2 , 3 ) ) >>> a array ( [ [ 0.6903007 , 0.39168346, 0.16524769], [ 0.48819875, 0.77188505, 0.94792155]]) >>> a .sum ( ) 3.4552372100521485 >>> a . min ( ) 0.16524768654743593 >>> a .max ( ) 0.9479215542670073 # specifying the axis parameter applies an operation along the s p e c i f i e d >>> b = arange ( 1 2 ) . reshape ( 3 , 4 ) >>> b array ( [ [ 0 , 1 , 2 , 3 ] , [ 4, 5, 6, 7] , [ 8 , 9 , 10, 1 1 ] ] ) >>> # sum of each column >>> b .sum( axis =0) array ( [ 1 2 , 15, 18, 21]) >>> # min of each row >>> b . min ( axis =1) array ( [ 0 , 4 , 8 ] ) >>> # cumulative sum along the rows >>> b .cumsum( axis =1) array ( [ [ 0 , 1 , 3 , 6 ] , [ 4 , 9 , 15, 22] , [ 8 , 17, 27, 3 8 ] ] ) Indexing, Slicing, Iterating Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language • One dimensional arrays can be indexed, sliced and iterated over pretty much like lists and other Python sequences. Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays >>> a = arange(10) ∗∗ 3 >>> a array ( [ 0 , 1, 8 , 27, 64, 125, 216, 343, 512, 729]) >>> a [ 2 ] 8 >>> a [ 2 : 5 ] array ( [ 8 , 27, 64]) >>> a [ : 6 : 2 ] = −1000 # modify elements in a >>> f o r i in a : ... print i ∗∗(1/3.) , ... nan 1.0 nan 3.0 nan 5.0 6.0 7.0 8.0 9.0 Indexing, Slicing, Iterating Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays • Multidimensional arrays can be with one index per axis. These indices are given in a tuple separated by comas >>> def f ( x , y ) : ... return 10∗x+y ... >>> b = fromfunction ( f , ( 5 , 4 ) , dtype= i n t ) >>> b array ( [ [ 0 , 1 , 2 , 3 ] , [10 , 11, 12, 13] , [20 , 21, 22, 23] , [30 , 31, 32, 33] , [40 , 41, 42, 4 3 ] ] ) >>> b[ 2 , 3 ] 23 >>> b [ : , 1 ] # the second column of b array ( [ 1 , 11, 21, 31, 41]) >>> b [ 1 : 3 , : ] # the second and t h i r d row of b array ( [ [ 1 0 , 11, 12, 13] , [20 , 21, 22, 2 3 ] ] ) • When fewer indices are provided than the number of axes, the missing indices are supposed to be complete slices >>> b[ −1] array ( [ 4 0 , 41, 42, 43]) # the l a s t row . Equivalent to b[ −1 ,:] Universal functions Python in Crystallography F. Otálora Introduction What is Python Comparisons The Language Numbers Strings Lists Dictionaries Tuples Assignment Control Structures Functions Modules Classes Misc ndarrays >>> p r i n t x [0 1 2 3 4] >>> p r i n t cos ( x ) [ 1. 0.54030231 −0.41614684 −0.9899925 −0.65364362] >>> p r i n t arccos ( cos ( x ) ) [ 0. 1. 2. 3. 2.28318531] # not a bug , but wraparound : 2∗ pi%4 i s 2.28318531 add divide_safe arccosh arctanh tanh sqrt ceil conjugate greater less logical_not bitwise_not subtract remainder arcsin cos log10 absolute fmod maximum equal less_equal logical_and bitwise_and multiply power arcsinh cosh sin fabs exp minimum not_equal logical_or bitwise_or divide arccos arctan tan sinh floor log greater_equal logical_xor bitwise_xor
Related documents