Python code snippets

misc - copy_array.py

a      =  [ 'one', 'two', 'three', 'four' ]

# Make a copy of a. Note: not a deep copy because references within
# point to the same object.
# In order to make a deep copy, use copy.deepcopy
#
a_copy = a[:]

# Create a reference to the array pointed at by 'a'.
a_ref  = a

a_copy.append('five')
a_ref .append('FIVE')

print(a_copy) # ['one', 'two', 'three', 'four', 'five']
print(a_ref ) # ['one', 'two', 'three', 'four', 'FIVE']
print(a     ) # ['one', 'two', 'three', 'four', 'FIVE']

misc - pass_by_value_or_reference.py

#/usr/bin/python
#
#  Does python pass by value or by reference?
#
#  Output of program is
#
#     B[two] = 2
#     B[one] = 1
#   
#

def f(X, k, v):
    X[k] = str(v)

A=dict()

f(A, 'one', 1)

B=A

f(A, 'two', 2)

for k in B:
    print "  B["+k+"] = " + B[k]


    

misc - callback_functions_with_arguments.py

def math_op(func, operand_1, operand_2): return func(operand_1, operand_2)

def plus(a, b): return a+b
def mult(a, b): return a*b


print (math_op(plus, 4, 5)) #  9
print (math_op(mult, 4, 5)) # 20

filecmp - script.py

import filecmp

if filecmp.cmp('a.txt', 'b.txt'):
   print "a.txt == b.txt"
else:
   print "a.txt != b.txt"

  
if filecmp.cmp('a.txt', 'c.txt'):
   print "a.txt == c.txt"
else:
   print "a.txt != c.txt"

libraries - Python-Image-Library - pixels.py

import Image

im = Image.new('RGB', (256, 256), "black")

pixels = im.load()

for     x in range(0, 256):
    for y in range(0, 256):

        pixels[x, y] = (x, y, 127)

im.show()
im.save('pixels.png')

statements - for_in.py

d = {'foo':  42, 
     'bar': "forty-two",
     'baz': None}

print
for k in d:
    print "  ", k, " = ", d[k]

print
print "Using items()"
for k,v in d.items():
    print "  ", k, " = ", v

statements - continue.py

for a in range(1, 10):

  # Don't print the numbers 5 and 7
    if a == 5 or a == 7: continue

    print a

statements - import - __import__.py

#!/usr/bin/python

FooBarBaz=__import__("FooModule")

print (FooBarBaz.module_func_sum(38,4)) # 42

statements - import - import_03.py

#!/usr/bin/python

import FooModule as f

print (f.BarModule.bar_func_4())

statements - import - from_X_import_ALL.py

#!/usr/bin/python

from FooModule import *

print module_func_sum (38,4)  # 42
print module_func_mult(21,2)  # 42

statements - import - import_02.py

#!/usr/bin/python

from FooModule import BarModule

print (BarModule.bar_func_4()) # 4

statements - import - BarModule.py

def bar_func_4():
    return 4

statements - import - from_X_import.py

#!/usr/bin/python3

from FooModule import module_func_sum

print(module_func_sum (38,4))                 # 42

# print FooModule.module_func_mult (38,4)     # NameError: name 'FooModule' is not defined
# print module_func_mult(21,2)                # NameError: name 'module_func_mult' is not define

statements - import - import_01.py

#!/usr/bin/python

import FooModule

print (FooModule.module_func_sum (38, 4))  # 42
print (FooModule.module_func_mult(21, 2))  # 42

print (FooModule.BarModule.bar_func_4())

# print module_func_sum(38,4)            # NameError: name 'module_func_sum' is not defined

statements - import - import_04.py

#!/usr/bin/python

from FooModule import *

print (module_func_sum(8, 9)) # 17

statements - import - FooModule.py

import BarModule

def module_func_sum(a, b):
    return a+b

def module_func_mult(a, b):
    return a*b

statements - pass.py

def X():
    pass

def Y():
    global y
    pass
    y = 42

X()
Y()
print y  # 42

standard-library - Tkinter - draw_image.py

# Note, Python 3 has lowercase Tkinter.
import Tkinter

tk     = Tkinter.Tk()
canvas = Tkinter.Canvas(tk, width = 200, height = 200)
canvas.pack()

canvas.create_rectangle( 20, 20, 180, 180, fill="orange")

canvas.create_line(  10,  10,  190,  190, fill="blue")
canvas.create_line(  10, 190,  190,   10)

Tkinter.mainloop()

standard-library - collections - script.py

#/usr/bin/python

import collections

cnt=collections.Counter()

for word in "foo bar baz more or less foo most foo even more foo or is it less".split():
    cnt[word]+=1

print "for word in cnt"
for word in cnt:
    print "  %-10s: %d" % (word, cnt[word])

print "\nfor word in cnt.most_common(3)"
for word in cnt.most_common(3):
    print "  %-10s: %d" % word

print "\nsum(): "
print "  There are " + str(sum(cnt.values())) + " words in the original string"

standard-library - site - script.py

#!/usr/bin/python

import distutils.sysconfig
import site
import sys

print "\nsite.getsitepackages():" 
for dir in site.getsitepackages():
    print "  " + dir

print "\n  Compare with distutils.sysconfig.get_python_lib():"
print "    " + distutils.sysconfig.get_python_lib()

print "\n  Compare alse with sys.prefix"
print "    " + sys.prefix

classes - member_variables.py

#!/usr/bin/python


class A(object):

  
  def __init__(self, ident):

      self.ident = ident
      foo        ='local variable'

  def go(self):
      
      print ("go " + self.ident)
#     print foo

a = A('aaa')

print a.ident    # aaa

# print a.foo    # AttributeError: 'A' object has no attribute 'foo'
# print foo      # NameError: name 'foo' is not defined

a.go()           # go aaa

builtin-functions - filter.py

def starts_with_b(t):
    return t[0] == 'b'
    

a = ['foo', 'bar', 'baz']

print filter(starts_with_b, a)
# ['bar', 'baz']

print filter(lambda t: t[0] == 'b', a)
# ['bar', 'baz']

print filter(None, [0, 'foo', None, 'bar', 'baz']) # Note: 0 and None will be gone...
# ['foo', 'bar', 'baz']

builtin-functions - map.py

for i in map(lambda λ: λ**2, range(6)):
    print(i)
    # 0
    # 1
    # 4
    # 9
    # 16
    # 25

builtin-functions - ord.py

# -*- coding: utf-8 -*-

ord_ = ord(u'־')
hex_ = format(ord_, '04x')

print str(ord_) + ' ' + str(hex_)

builtin-functions - len.py

a = ['one', 'two', 'three', 4, 5]
print len(a) # 5

d = {'foo': 'one', 'bar': 2, 'baz': None}
print len(d) # 3

See also