Download Intro To Python - University of Virginia Library

Intro To
Pete Alonzi
University of Virginia Library
Research Data Services
February 14, 2017
Outline
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Installation
Getting our sea legs – terminals, and text editors, and IDEs
Math and variables
Functions
Python Data Types
Loops
Logic
Import
Odds and ends
Installation of Python
• Two Notes
– Language (python) vs language distribution (anaconda)
– Python 2 vs Python 3
• https://www.continuum.io/downloads
Programming vs Python
• For this workshop we are not requiring any
previous knowledge of python or of computer
programming. As a result we will be explaining
fundamental concepts of each. Our emphasis
is on the python but we will spend time on
programming as well.
Brief history of Python - https://www.python.org/
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Designed by Guido van Rossum
1991
successor to the ABC language
Python 2.0 was released on
16 October 2000
• Python 3.0 was released on
3 December 2008
Let’s Open Spyder
Programs – “Hello World!”
• In programming the classic first program is
called “Hello World!”
Math and Variables
• Python knows math!
– 1+2
• Python uses variables to reference things (for
example some math).
– X = 1+2
Variable
The “=“ is special. It doesn’t mean
equals to. It means refers to.
Math and Variables
• Math operations
o + - * / ** % //
• Variable rules
o Must start with a letter
o Have a type
Functions
• Functions are prewritten pieces of code that
perform one specific task.
• Let’s take a look at type(…)
name
Function code
arguments
Programs – “Hello World!”
• In programming the classic first program is
called “Hello World!”
Data Types - Strings
• A string is a string of characters
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“apple”
“blue42”
“iamtheverymodelofamodernmajorgeneral”
“7hills”
• Helper functions: string.lower(), string.upper()
– And many more, check out the online docs
Indexing
fruit = ‘ a p p l e ‘
0 1 2 3 4
-5 -4 -3 -2 -1
Data Types – Strings - Slicing
• Reference elements of a string with […:…]
– [from:up to but not including]
Data Types - Lists
• Lists are represented: name[…]
– Contains a list of elements of various types
– You can even have a list of lists
– Lots of helper functions
– Reference with [...] and can slice too!
Don’t forget tuples: name(…) and immutable
Data Types - Dictionary
• Dicts are represented: name{…}
– Elements are a pair: key:value
– The keys are strings and values are anything
– Lots of helper functions
Loops – FOR
• For loop syntax: for ___ in ___ :
– The first blank is a new variable
– The second blank is an iterable
– eg: for x in range(10): print x
Loops – WHILE
• While loop syntax: while <boolean>:
– The boolean is checked every iteration
– eg: while i<10: print i; i+=1
If statements
• Normally your code progresses linearly
• Use an if statement for a fork in the road
• Syntax: if <boolean>: ______
else: _______
• To chain multiples together use elif
Import modules
• A great feature of python is modularity. Lots of
people have developed lots of good modules.
• A great module is called numpy
– Eg: numpy.random.randn()
• But my favorite module is called pandas
• Use nltk for text manipulation
Import modules
• A great feature of python is modularity. Lots of
people have developed lots of good modules.
• A great module is called numpy
– Eg: numpy.random.randn()
• But my favorite module is called pandas
Comments
• Every programming language has a way for
you to include text to help explain the code.
• In python you can make a comment two ways.
– # everything after a # is commented
– Everything between ’’’ is a comment ‘’’
File input/output (I/O)
• Reading from a file
File input/output (I/O)
• Writing to a file