Download Duck Typing - itk.ilstu.edu

Documentation / References
• Python Full Documentation
– http://docs.python.org/index.html
• Python Quick Reference
– http://rgruet.free.fr/
• IPython
– <object>?
– help <object>
– tab completion
Basics
• Tabbing is crucial and mandatory
– DO NOT mix tabs with spaces, choose one method and stick to it
• Comments:
– # single line comment
– """ long comment """
• Philosophic mindset
– Shorter and simpler is better, without getting cryptic
– Intuitive to existing programmers
– No deliberate way to do the same code in two different ways
• Keywords
–
–
–
–
None
True
False
pass
Duck Typing
•
•
“when I see a bird that walks like a duck and swims like a duck and quacks like a duck, I
call that bird a duck.” - James Whitcomb Riley
Static Typing
Duck Typing (Dynamic)
Dynamic Typing
C/C++/C#
Java
Python
Perl
PHP
Ruby
Casting:
–
int(variable)
–
float(variable)
•
•
–
•
int('FF', 16) == 255
also definable by adding a period
str(variable)
Type Comparison
–
–
–
type(variable) == type([])
type(variable) == type(“”)
type(variable) == type(0)
Data Types
• Modules
• Objects
–
–
–
–
–
–
Integer
Float
Strings
List
Dictionary
Tuple
• Decorators
• Generators
Modules
• Two methods of importing
• import math
– Now, functions or attributes defined in math can be
accessed like so: math.pi, math.sin(), etc.
• from math import *
– Now, all of math is imported into the global
namespace and can be accessed like so: pi, sin(), etc.
• from math import pi
– Now, only pi is in the global namespace
Numbers
• Types:
– Integers
– Floats
• Infinite length
• Math
– (+-*/%^&|)
– ** instead of ^ (but ^ exists as XOR, be careful)
– += exists, but ++ does not (use +=1)
• More math
– import math
– math.e, math.pi, math.cos(), math.acos(), math.cosh(),
math.log(), math.ceil(), math.sqrt()
Control Flow Statements
•
•
•
if, elif, else… and, or, not
while
list = [2, 3, 1, 7]
i = 0
– continue
while i < len(list):
– break
print "output:",
i += 1
for
– More like foreach in other languages
list = [2, 3, 1, 7]
for x in list:
print "output:”, str(x)
•
try, except
try:
dict_array[0]['item’]
# code for success
except IndexError:
# code if [0] fails
except KeyError:
# code if ['item'] fails
str(i)
output:
output:
output:
output:
output:
output:
output:
output:
2
3
1
7
2
3
1
7
if len(dict_array) == 0:
# code if [0] fails
elif dict_array.has_key('item‘):
# code if ['item'] fails
else:
# code for success
switch Control Structure
• There isn’t one.
• Alternatives to switch:
– if, elif, else
if var == 'one':
# do 'one' specific code
elif var == 'two':
# do 'two' specific code
elif var == 'three':
# do 'three' specific code
else:
# do default code
– dictionary forms
{'one': lambda x: x+1,
'two': lambda x: x+2,
'three': lambda x: x+3
}[var](var)
def one_code():
# do 'one' specific code
def two_code():
# do 'two' specific code
def three_code():
# do 'three' specific code
def default_code():
# do default code
{'one': one_code,
'two': two_code,
'three': three_code}[var]()
Strings
• Defined in usual ways
• Important Methods:
– strip()
– join()
– split()
mystr = " first second third"
myarr = mystr.strip().split(" ")
for i in xrange(0, len(myarr)):
print "output:", myarr[i]
print "mystr::%s::" % " ".join(myarr)
output: first
output: second
output: third
mystr::first second third::
• String formatting (like printf)
Lists
• Important methods
– append()
– extend()
– insert()
– pop()
list = [3, 4, 5]
print "pop: %d" % list.pop(1)
list.insert(0, 2)
list.append(6)
list.extend([7, 8])
print "list: %s" % str(list)
pop: 4
list: [2, 3, 5, 6, 7, 8]
Slicing
• A more complex way of handling list items and
strings
list = [2, 3, 1, 7, 5]
print
print
print
print
print
list
list[1:2]
list[2:]
list[-2:]
list[:-2]
[2,
[3]
[1,
[7,
[2,
3, 1, 7, 5]
7, 5]
5]
3, 1]
Tuple
• Collection of a fixed amount of values
• Tuple unpacking
def output_three_multiples(self, number):
return (number*2, number*3, number*4)
(first,second,_) = output_three_multiples(7)
File Manipulation
• First thing that made me like Python
file = open("filename", "r")
contents = file.read()
file.close()
print contents
file = open("filename", "r")
contents = file.readlines()
file.close()
line_num = 1
for line in contents:
print "%d: %s" % (line_num, line)
line_num += 1
Classes
• Everything involving classes in Python is weird
• All classes extend "object"
– Like Java
– Historically this was not the case, so be careful
• Constructor is: def __init__(self):
• Private methods prefixed with two underscores
• Static methods use @staticmethod decorator
• Super methods are weird, too
Class Code
import attrdict
import errors
from execute import *
class server(attrdict):
def __init__(self, dict):
super(server, self).__init__(dict)
# no executer until a function makes one
self.executer = None
def __do_execute(self, cmd):
ret = self.require_remote()
if ret: return (None,None,None)
if self.executer:
return self.executer.execute(cmd)
else:
return execute_srv(self.remote_server, cmd)
def require_remote(self):
if not self.require_dict(self.remote_server, [
"ip",
"port"
]):
return errors.throw(errors.BACKEND_INVALID_INPUT)
Class Code 2
import errors, glob, server
from execute import *
class master(server):
def __init__(self, dict):
super(master, self).__init__(dict)
@staticmethod
def __do_execute(cmd):
return execute(cmd)
def remove_key(self):
ret = self.require_remote()
if ret: return ret
# strip keys from remote server
(exit_code,_,_) = self.__do_execute(
"ssh -i %s " % glob.config.get("paths", "master_private_key") +
"-p " + str(self.remote_server['port']) + " root@" +
self.remote_server['ip'] + " " +
"\"sed -r \\\"/^.*_panenthe$/d\\\" -i %s\"" %
glob.config.get("paths", "user_ssh_authorized_keys")
)
# fail
if exit_code != 0:
return errors.throw(errors.SERVER_REMOTE_REMOVE)
# return
return errors.throw(errors.ERR_SUCCESS)
Libraries
Name
Function
Tkinter
TK graphics
os
POSIX functions & operating
system generic functions
re
Regular expressions (close to
PCRE)
sys
Information about current
instance and system (I.E.
arguments to command line,
exit(), etc.)
urwid
curses/ncurses frontend with
common widgets