Python

links

http://en.wikibooks.org/wiki/Non-Programmer%27s_Tutorial_for_Python_2.6
http://docs.python.org/tutorial

Reference

http://docs.python.org/ref/ref.html
http://docs.python.org/library/

basics

print "Hello, World!"

command called print followed by one argument,which is "Hello, World!". (referred to as a string of characters, or string) Command and its arguments are collectively referred to as a statement,

print "2 + 2 is", 2 + 2

The first argument is the string "2 + 2 is" and the second argument is the mathematical expression 2 + 2, which is commonly referred to as an expression. each of the arguments separated by a comma

Print without spaces. flush buffers.

import sys
sys.stdout.write(character)
sys.stdout.flush()

sys.argv   arguments are passed to the script in the variable sys.argv
#          is used to start a comment

Enable swedish keys åäö

#!/usr/bin/python
# -*- coding: utf-8 -*-

operations for numbers

Operation	Symbol	Example
Power (exponentiation)	**	5 ** 2 == 25
Multiplication	*	2 * 3 == 6
Division	/	14 / 3 == 4
Remainder (modulo)	%	14 % 3 == 2
Addition	+	1 + 2 == 3
Subtraction	-	4 - 3 == 1

userinput

raw_input (returns a string)

user_reply = raw_input("Who goes there? ")

input (returns digits)

number = input("Type in a number: ")

type(number) (tells what a variable is.)

print "number is a", type(number)

while loop

print number interval. finish while loop with a ':' The while statement only affects the lines that are indented with whitespace.

start = input("Start number? ")
stop = input("Stop number? ")
a = start
while a < stop:
    print a
    a = a + 1

operator	function
<	less than
<=	less than or equal to
>	greater than
>=	greater than or equal to
==	equal
!=	not equal
<>	another way to say not equal (old style, not recommended)

if statment

 if a > 5:  
   print a, ">", 5
 elif a <= 7:
   print a, "<=", 7
 else:
   print "Neither test was true"

1. This Program Demonstrates the use of the == operator # using numbers

print 5 == 6 

false

functions

The key feature of this program is the def statement. def (short for define) starts a function definition. def is followed by the name of the function absolute_value. Next comes a '(' followed by the parameter n (n is passed from the program into the function when the function is called). The statements after the ':' are executed when the function is used. The statements continue until either the indented statements end or a return is encountered. The return statement returns a value back to the place where the function was called.

def absolute_value(n):
  if n < 0:
    n = -n
  return n

import

command import loads a module

Sleep

import time
time.sleep(secs)

random

import random
number = random.randrange(1, 100, 1)

deepcopy

To copy lists that contain lists use deepcopy

import copy
c = copy.deepcopy(a)

list

list with more than one value.

which_one = input("What month (1-12)? ")
months = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December']
if 1 <= which_one <= 12:
 print "The month is", months[which_one - 1]

Print a whole list.

demolist = ["life", 42, "the universe", 6, "and", 7]
print "demolist = ",demolist

demolist = ['life', 42, 'the universe', 6, 'and', 7]

b = a

makes b a reference to a.

b = a * 1
b = a[:]

copies b to a.

operations

example	explanation
demolist[2]	accesses the element at index 2
demolist[2] = 3	sets the element at index 2 to be 3
del demolist[2]	removes the element at index 2
len(demolist)	returns the length of demolist
"value" in demolist	is True if "value" is an element in demolist
"value" not in demolist	is True if "value" is not an element in demolist
demolist.sort()	sorts demolist
demolist.index("value")	returns the index of the first place that "value" occurs
demolist.append("value")	adds an element "value" at the end of the list
demolist.remove("value")	removes the first occurrence of value from demolist (same as del demolist[demolist.index("value")])
onetoten = range(1, 11)
list[-1]	Returns the last index
list[-2]	Returns the second last index
things[4:7]	Pick slice of list

functions

ord()        Returns a character as a number. 
chr(15)      Return number to character
repr()       Convert a integer to a string
int()        Convert a string to an integer.
float()      Convert a string to a float
eval()       Takes a string and returns type that python thinks it found
text.split(",")    converts a string into a list of strings. The string is split by whitespace by default or by the optional argument You can also add another argument that tells split() how many times the separator will be used to split the text.

for loop

demolist = ['life', 42, 'the universe', 6, 'and', 9, 'everything']
for item in demolist:
   print item

dictionary

Add an empty dictonary called words

words = {}

Create a list of keys in dictionary.

for x in words.keys():

Grabs the words in a dictionary. Print meaning of word

print words[x]

If name exist in dictionary, remove it.

if name in words:
 del words[name]

File IO

1. Write a file

out_file = open("test.txt", "w")
out_file.write("This Text is going to out file\nLook at it and see!")
out_file.close()

1. Read a file

in_file = open("test.txt", "r")
text = in_file.read()
in_file.close()

1. Read file if it exists.

import os 
filename = os.environ.get('PYTHONSTARTUP') 
if filename and os.path.isfile(filename):
  execfile(filename)

error handling

try:
number = int(raw_input("Enter a number: "))
 print "You entered:", number
except ValueError:
 print "That was not a number."

Try handles error handling. If you didn't get a number ask for one.

1. How to configure python. Where should I put config file.

import site site.getusersitepackages() /home/user/.local/lib/python3.2/site-packages'

1. create file /home/user/.local/lib/python3.2/site-packages/usercustomize.py
2. /home/user/.local/lib/python3.2/site-packages/sitecustomize works in the