Python Learning Part -1

Indexing and slicing with strings : 

string = 'abcdefghijk'

string[STARTING_INDEX_POSITION:GO_UPTO_INDEX_POSITION] 

string[2:] //output cdefghijk

string[:3] //output abc note-> it says goes upto the index d but not include the index d

string[3:6] // output def

String Concatenation :

name = 'Amar' 

lname = 'Singh'

fname = name + lname // output Amar Singh

Lost of string inbuild functions are there you can check and explore them like

name.split() // ['Amar','Singh'] // split the string based on the white space

Print Formatting with String :

Format A string with .format()

Input : print('my name is {}'.format('Dharmendra'))

output : my name is Dharmendra

Lists in Python:

• lists are ordered sequences which holds variety of object types.
• they use [] and , to separate it
• list support index & slicing 
  

 like [1,2,3,4,5]

mylist = [1,2,3,4,5]

mylist[1:] //[2,3,4,5]

has some inbuild functions like .pop, .sort etc

Dictionaries in Python :

•  dictionaries are unordered mappings for storing objects
• it uses as a key value pairs

my_dist = {'key1' : 'value1','key2' : 'value2'} 

 

Difference between lists and dictionaries:

Dictionaries : Object retrieved by key name,Unordered and can't sorted

Lists : Object retrieved by location, ordered sequences can be indexed or sliced.

 Tuples in Python :

• Tuples are very similar to lists , However they have one key differences - immutability (means we can not change the value of any index)
• once an element is inside tuples , it can not reassigned 
• tuples uses parenthesis: like (1,2,3,4,5)

Sets in Python : 

• sets are unordered collection of unique collections
• only unique value we can put inside it.
• like {1,2}
  

mylist = [1,1,1,2,2,3,3,3,1,2]

set(mylist) // output {1,2,3}

Python Statements

if else statement : 

if 3 == 2 :
    print('No')
elif 3 == 3 :
    print ('Yes')
else :
    print ('Do not know')

For Loop : 

list1 = [1,2,3,4,5,6,7,8,9,10]

for num in list1:
    print(num) // it will print number 1 to 10 

we can run for loop for anykind of data like string,tuples,sets,lists etc.

2nd example :

d = {'k1':1,'k2':2,'k3':3}

for item in d:
    print(item)  // k1 k2 k3

 While Loop:

x = 0

while x < 10:
    print('x is currently: ',x)
    print(' x is still less than 10, adding 1 to x')
    x+=1

 Useful Operators:

There are a few built-in functions and "operators" in Python

range : 

list(range(0,11))

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

enumerate:

for i,letter in enumerate('abcde'):
    print("At index {} the letter is {}".format(i,letter))

//output

At index 0 the letter is a
At index 1 the letter is b
At index 2 the letter is c
At index 3 the letter is d
At index 4 the letter is e 

 

zip:

list(enumerate('abcde')) 

//R: [(0, 'a'), (1, 'b'), (2, 'c'), (3, 'd'), (4, 'e')]

mylist1 = [1,2,3,4,5]
mylist2 = ['a','b','c','d','e']

zip(mylist1,mylist2)

list(zip(mylist1,mylist2))

//R: [(1, 'a'), (2, 'b'), (3, 'c'), (4, 'd'), (5, 'e')]

in operator:

'x' in ['x','y','z']

// TRUE

'x' not in ['x','y','z']

//False  

min and max:

mylist = [10,20,30,40,100],    

min(mylist) ://10

max(mylist) :// 100

random & Input also there you can check from git source.

 

List Comprehensions

In addition to sequence operations and list methods, Python includes a more advanced operation called a list comprehension.

lst = [x for x in 'word'] 

lst :// ['w', 'o', 'r', 'd'] 

Map and Filter Functions : The map function allows you to "map" a function to an iterable object.

def square(num):
    return num**2 

my_nums = [1,2,3,4,5]

map(square,my_nums)

list(map(square,my_nums))
 //output 

[1, 4, 9, 16, 25]

Filter Function : Meaning you need to filter by a function that returns either True or 
False. Then passing that into filter (along with your iterable) and you 
will get back only the results that would return True when passed to the function.

 list(filter(check_even,nums))

 

 

 

 

 

 

 

 

Ref : https://github.com/Dharmend/Complete-Python-3-Bootcamp