if myString.endswith(mySubString) :
	# Do something

How to do it in C++

bool endswith(string myString, string mySubString)
{
	if(myString.length()>=mySubString.length())
	{
		string mySteingEnd = myString.substr(myString.length()-mySubString.length(),mySubString.length());

		if(myStringEnd.compare(mySubString)==0)
			return true;

		else
			return false;
	}

	return false;
}

How to do it in Python

int myInt = 9 ;
string myString = "Srajan" ;

myInt = 9
myString = "Rishabh"

Hello World!

print "Hello World!"

That's it! No need to load libraries or define functions.

Some basics :

Python code can be written in  any text editor. It just needs to be saved as a .py file.

Only one statement on one line. You can use semicolon to write multiple statement on one line, but it is usually not recommended to do so.

Variables are assigned just like in C++ , but they don't need to be previously declared or have type. 

myInt = 1
myString = "Hello"
myBool = False ; myFloat = 3.1415

Placeholders

Similar to format specifiers in C++, we use placeholders like %s and %d for string and numerical values respectively, in the print statement.(You can also use +, to seperate variables)

name = "Shantanu"
num = 420
print "%s %d" % (name,num)
# Shantanu 420
# Works as expected!

Single line comments are preceded by '#'. While multi-line comments are enclosed between ''' (three single quotes)

print "Not a comment"
# I'm  a comment
'''I'm a multi
line comment
'''

Basic operations

x, y = 3, 2 # multiple assignment
print x + y # 5 
print x - y # 1
print x * y # 6
print x / y # 1, in Python 2.7, truncates the answer
print x ** y # 9, x raised to the power of y

In python, its's very easy to convert one type of data type to another. We use type casters. You can use type() to get the type of the var.

myStr = "5"
myInt = 5

print myStr + myInt
# Type error returned.
print int(myStr) + myInt
# 10

print int(5.0/3)
# 1 , float -> int 
print str(3)
# "3" , the string not the int.
print type("3")
# <type 'str'>
print type(3)
# <type 'int'>
print type(3.0)
# <type 'float'>

Input from user

In python 2.7, there are two methods to take user input. raw_input and input.

myVar = raw_input("Enter variable :")
# Will prompt user to input, and the input will be stored as string
# say we entere " 3*4 "
print myVar
# 3*4
myVar = input("Enter variable :")
# Tkes the input and tries to evaluate it, if possible
# say we input 3*4
print myVar
# 12

The conditionals in python are very similar to C++. Instead of using {} use indented blocks.

if a > b :
	print "a is greater than b"
elif a==b :
	print "both are equal"
else :
	print "b greater than a"

Be careful of the indentation and the colon.

Functions

In python,there is no need to mention the 'types' of arguments or return type of the function. You must define it before use, in your program. Passing of variables is 'by value' except for mutable objects (like lists).

def thankYou(name = "Srajan") :

	print "Thanks " + name
	return

thankYou("Rishabh")
# Thanks Rishabh
thankYou()
# Thanks Srajan

The list is a versatile datatype available in Python which can be written as a list of comma-separated values (items) between square brackets. Important thing about a list is that items in a list need not be of the same type. Also, lists are mutable objects. When passed in functions as parameters, they are passed by reference.

They are similar to "vectors" as defined in the C++ STL library.

colors = ["Green","Red","Yellow","Blue"]
# Here colors is a list, with all string elements

numbers = range(2,7)
# range is an inbuilt function
# numbers = [2,3,4,5,6]

Accessing a list

print colors[0]
# Green
print colors[-1]
# Blue
print len(colors)
# 4

Iterating in a list

for color in colors :
    print color
# Green
# Red
# Yellow
# Blue

This is a for loop, and the variable 'color' is like an placeholder iterator. Basically python will place each item of the list into this variable,one at a time.

Splicing

# colors = ["Green","Red","Yellow", "Blue"]
colors[start:end] 
# items start through end-1

print colors[0:2]
# ["Green" , "Red"]

print colors[:-1]
# ["Green", "Red", "Yellow"]

print colors[0:len(colors)]
# Basically the whole list

Modifying Lists

# colors = ["Green","Red"]

colors.append("Purple")
print colors
# ["Green","Red","Purple"]

colors.insert(1,"Brown")
print colors
# ["Green","Brown","Red","Purple"]

del colors[1]
# ["Green","Red","Purple"]

colors.remove("Purple")
# ["Green","Red"]

colors.pop()
# ["Green"]

Comprehension

# Make a list of the first five even numbers.
evens = [number*2 for number in range(1,6)]
# evens = [2,4,6,8,10]

# Copying a list
b = [ a[i] for i in range(len(a)) ]

Min/Max and sum

# nums = [1,3,4,0,2]
print sum(nums)
# 10
print min(ans)
# 0
print max(ans)
# 4

# for string, min/max searches alphabetically

Making a list from another

# xyz = ["x","y","s","z"]
print xyz.index("s")
# 2
print xyz.index("A")
# ValueError "A" not in list

a = range(5,0,-1)
# a = [5,4,3,2,1]
a.sort()
# sorts in ascending/alphabetical order
print a
# a = [1,2,3,4,5]

import random
# a = range(5)
random.shuffle(a)
print a
# [0,2,3,4,1]

# a = [4,2,3,1]
a.sort()
print a
# [1,2,3,4]

# a = [2,3,4,5,1]
a.reverse()
print a 
# [1,5,4,3,2]

Concatenation

Basically joining of two strings

# string1 = "a"
# string2 = "bc"
print string1 +string2
# abc

str = "-";
seq = ("a", "b", "c");
print str.join( seq );
# a-b-c

Find/Replace

str1 = "this is string example"
str2 = "exam"

print str1.find(str2)
# 15
print str1.find(str2, 20)
# searching after index 20
# -1

str = "this is is a string"
print str.replace("is", "was")
# thwas was was a string
print str.replace("is", "was", 2)
# 2 is the max number of replacements
# thwas was is a string

# can also use 'in'
if substr in string:
    # do this

a = '    b c d   '
a.strip()
# removes spaces in the beggining/end of string
print a
# 'b c d'
a = 'this,is a sentence,that i want,to break'
a.split(" ") 
# returns list of elemtts seperated by " "
print a.split(" ")
# ["this,is","a","sentence,that","i","want,to","break"]
print a.split(",")
# ["this","is a sentence","that i want","to break"]

Other functions

# string = "hello"
print string.capitalize()
# Hello

print string.islower()
# False

print string.isnumeric()
# False

# Raw strings
simpleString = "hello\n world"
rawString = r"hello\n world"

print simplestring
# hello
#  world

print rawSting
# hello\n world

# Also place a "u" instead
# of "r" for unicode strings

Raw/Unicode

Closure

A Closure is a function object that remembers value in enclosing space regardless of whether those scopes are present in memory or not.

def startAt(start):
	def incrementBy(inc):
		return start + inc
	return incrementBy

f = startAt(10)
g = startAt(100)

print f(1), g(2)

# 11 102

Basically, here incrementBy is a closure. In this case both f and g are references to the nested function incrementBy

Lambdas

Lambdas are anonymous throwaway functions. They are just needed where they have been created. Mostly used with other function such as filter(), map() and reduce()

def startAt(start):
	return lambda inc : start+inc

f = startAt(10)
g = startAt(100)

print f(1), g(2)

# 11 102

# Format of a lambda function
# lambda args list : expression

f = lambda x,y : x + y
print f(1,1)
# 2

Basically map(), applies a particular function to each element of a list and return the answers as a list too.

# Syntax

returnedList = map(func,list)

Celsius = [39.2, 36.5, 37.3, 37.8]
Fahrenheit = map(lambda x: (float(9)/5)*x + 32, Celsius)
print Fahrenheit

# [102.56, 97.7, 99.14, 100.04]
# Here we used a lambda function

# Can be more complex
a = [1,2,3,4]
b = [17,12,11,10]
print map(lambda x,y:x+y, a,b)

# [18, 14, 14, 14]

filter()

filter() is used to filter out elements in a list using a boolean function. It returns a list, after applying the function to every element in the list.

# Syntax

returnedList = filter(boolFunc,list)

# we filter out the odd numbers

fib = [0,1,1,2,3,5,8,13,21,34,55]
result = filter(lambda x: x % 2, fib)
print result
# [1, 1, 3, 5, 13, 21, 55]

dictionary_name = {key_1: value_1, key_2: value_2, key_3: value_3}

# Example
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}

print dict
# {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
print dict.items()
# [('Name': 'Zara'), ('Age': 7), ('Class': 'First')]
# A list of tuples

Basic operations

print dict["Age"]
# 7

# Iterating over dictionaries

for key,value in dict.items():
    print key + ":" + value
# Name:Zara
# Age:7
# Class:First

# Another iteration
for key in dict.keys():
    print key + ":" + dict[key]

# Same as before

# Modifying values

dict["Age"] = 8

# Adding values
dict["School"] = "DPS"

print dict
# {'Name': 'Zara', 'Age': 7, 'Class': 'First', 'School':'DPS'}

# Deleting elements
del dict["Age"]

print dict
# {'Name': 'Zara','Class': 'First', 'School':'DPS'}

# Zipping

x = [1, 2, 3]
y = [4, 5, 6]
zipped = zip(x, y)

print zipped
# [(1, 4), (2, 5), (3, 6)]

# We can also make a dictionary

dict = { key:value for k,v in zip(x,y)}

# Unzipping

list = [(1,2), (3,4), (8,9)]
unzipped = zip(*list)
print unzipped

# [(1, 3, 8), (2, 4, 9)]

# if we want a list of lists

unzipped = map(list,zip(*list))