quick & dirty basic python reference - v1

this is definitely not a tutorial. just quick notes I took while reading two python books and playing with this nice&flexible language.

http://diveintopython.org/toc/index.html

Getting around:

Get help:

>>> num = 10

>>> help(10)

Help on int object:

class int(object)

| int(x[, base]) -> integer

|

| Convert a string or number to an integer, if possible. A floating

| point argument will be truncated towards zero (this does not include a

| string representation of a floating point number!) When converting a

| string, use the optional base. It is an error to supply a base when

| converting a non-string.

|

| Methods defined here:

|

| __abs__(...)

| x.__abs__() <==> abs(x)

|

| __add__(...)

| x.__add__(y) <==> x+y

.

.

.

Basic commands and concepts:

>>>print 2*3

6

>>> x = 2

>>> x += 1

>>> x

3

>>> 2 ** 3 #power

8

>>>TextFromUser = raw_input( )

import sys - imports system library

sys.path.append - appends a floder to python path

if "somevalue" in sys.argv: - nice way to write an if statement when asking about a list item

reload(someScript) - reloads a script\library

from datetime import datetime.current - imports a specific function/member

from SomeScript import var1 , var2 , var3 , var4 - imports a specific function/member

>>> import random

>>> random.random( )

0.232425325

>>> random.choice([1,2,3,5,8,13,21,34,55])

13

>>> userdata = int(input("how old are you")) #get input from user

how old are you54

>>> userdata

54

Get a list of type's\object's function:

>>> dir(list)

['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

>>> lst = [1,2,3,4,5]

>>> dir(lst)

['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

Data types:

string:

>>> S = 'stringy'

>>> S[1]

't'

>>> S[-2]

'g'

>>> S[1:4]

'trin'

>>> S[1:]

'tringy'

>>> S[:2]

'st'

>>> len(S)

7

>>> S*3

'stringystringystringy'

#this is how we create multi-line string

os.environ["CFLAGS"] = "-W -Wimplicit-int " + \

"-Wimplicit-function-declaration " + \

"-Wimplicit -Wmain -Wreturn-type -Wunused -Wswitch "

Dictionary:

>>> dict = {'felix':'cat','rex':'dog','num':2}

>>> dict['num'] -= 2

>>> dict['num']

0

list:

>>> lst1 = [1,2,3,4,5]

>>> lst1

[1, 2, 3, 4, 5]

>>> lst1[1:]

[2, 3, 4, 5]

>>> lst1[:-1]

[1, 2, 3, 4]

>>> lst1[-3:]

[3, 4, 5]

>>> lst2 = [1,2,[1,2,3,4],1,1,2,2]

>>> lst2[2]

[1, 2, 3, 4]

>>> lst2.append(1)

>>> lst2

[1, 2, [1, 2, 3, 4], 1, 1, 2, 2, 1]

>>> lst3 = lst2 * 2

>>> lst3

[1, 2, [1, 2, 3, 4], 1, 1, 2, 2, 1, 1, 2, [1, 2, 3, 4], 1, 1, 2, 2, 1]

>>> lst4 = [11,22,33,44,55]

>>> lst4.pop(1)

>>> lst4

[11,33,44,55]

>>> multidimlist = [[1, 2, 3],

[4, 5, 6],

[7, 8, 9]]

>>> multidimlist[1][1]

5

>>> multidimlist = [[1,2,3],[4,5,6],[7,8,9]]

>>> [row[0] for row in multidimlist]

[1, 4, 7]

>>> [{row[0],row[1]} for row in multidimlist if row[0] > 3 and row[1] < 9]

[set([4, 5]), set([8, 7])]

tuple: (same as list just immutable):

>>> tup = (1,1,1,1,1,1,2,2,2,3,4,5,6)

>>> tup.count(2)

3

Set:

>>> s1 = set([1,2,3,4,5])

>>> s2 = set([3,4,5,6,7,8])

>>> s1 & s2

set([3, 4, 5])

>>> s1 - s2

set([1, 2])

>>> s2 - s1

set([8, 6, 7])

>>> s1 | s2

set([1, 2, 3, 4, 5, 6, 7, 8])

type: (for 'reflection\introspection' operations)

>>> sample_set = set([1,2,3])

>>> type(sample_set)

http://diveintopython.org/power_of_introspection/index.html

class:

class hunter:

def __init__(self,name,age): #init when created

self.name = name

self.age = age

def hunt(self,animal):

return str(animal) + " hunted"

>>> jack = hunter.hunter('jack',22)

>>> jack.hunt('joe')

'joe hunted'

Functions:

Define a function:

>>> def fact(n):

""" calculates the factorial """

r = 1

while n >0:

r = r*n

n = n - 1

return r

Run the function:

>>> fact(4)

24

Define a function with named parameters and with default values:

>>> def myPower(arg1 , arg2=2):

x = 1

counter = arg2

while counter > 0:

x = arg1 * x

counter = counter - 1

return x

Run the function:

>>> myPower(3)

9

>>> myPower(2,8)

256

>>> myPower(arg2 = 8 , arg1=2)

256

Define a function undefined number of args:

>>> def Contains10(*nums):

current = 0

for num in nums:

if num == 10:

return 'true'

return 'false'

Run the function:

>>> Contains10(10,22)

'true'

>>> Contains10(1,2,3)

'false'

Function is a first class citizen - can be passed as a parameter or set to a variable:

>>> ct = Contains10

>>> ct(10,2,3)

'true'

Function that gets another function as argument and returns a new funcion - decorator pattern:

>>> def logTime(func):

from datetime import datetime

print("setting time logging decoration to ", func.__name__)

def wrapperFunc(*args):

print("start " , func.__name__, " - " , datetime.now())

func(*args)

print("finish " , func.__name__, " - " , datetime.now())

return wrapperFunc

Apply decorator to a function:

>>> @logTime

def takesLongTime():

i = 0

while i < 1000000000:

i += i + 2

return i

setting time logging decoration to takesLongTime

Run the function:

>>> takesLongTime()

start takesLongTime - 2011-09-08 00:42:33.682000

finish takesLongTime - 2011-09-08 00:42:33.710000

Working with files\web\database:

working with files:

>>> f = open('c:\example.txt', 'w')

>>> f.writelines('I am the first line')

>>> f.write('I am some more text')

>>> f.close()

the file now contains -> "I am the first lineI am some more text"

>>> f = open('c:\example.txt')

>>> f.read()

'I am the first lineI am some more text'

>>> import os

>>> for root, dirs, files in os.walk('c:\\playpython'):

print("{0} has {1} files".format(root , len(files)))

c:\playpython has 6 files

c:\playpython\1dir has 1 files

c:\playpython\2dir has 6 files

Working with web client: (urllib2)

http://docs.python.org/library/urllib2.html

>>> import urllib2 as u

>>> webpage = u.urlopen('http://www.cnn.com')

>>> webpage.read(400)

' \nWorking with mongodb:

http://api.mongodb.org/python/2.0.1/tutorial.html

>>> import pymongo

>>> from pymongo import Connection

>>> conn = Connection('localhost', 666) #connect to mongodb on local machine over port 666

>>> db = conn('myDB) #open specific db inside mongodb server

>>> collection = db.customers #get a specific collection