# Python 01
###### tags: `mobile-development` `backend`

Let’s glide through all the basic concepts in Python :
## To give single or multi-line comment use:

#single line comment 

""" this is a
multi-line 
comment"""

## We can declare variables directly in Python without putting any data type unlike other languages like C/C++.

x = 8
y = "variable"
print(x) #to print a statement 
print(y)

a , b = "Hello" , "World"  #to assign values in single line 
print(a)
print(b)

## To get the data type of any object:

x = 8
print(type(x))

## Basic operations in Python:

a = 4 
b = 9
print(a+b) #addition
print(a-b) #subtraction
print(a/b) #division
print(a*b) #multiplication
print(a**b) #exponentiation

## The basic data structures in Python are:

* `List`: An ordered collection that is changeable and allows duplicate members.
* `Tuple`: An ordered collection that is unchangeable and allows duplicate members.
* `Set`: An unordered and unindexed collection doesn’t allow duplicate members.
* `Dictionary`: An unordered collection that is changeable and indexed. Also, it doesn’t allow duplicate members.

a = ["Hello", "World", "!"]    #List
b = ("Hello", "World", "!")    #Tuple
c = {"Hello", "World", "!"}    #Set
d = {"name" : "Suraj", "age" : 18, "location": "India"}    #Dict

## To understand the data structures in detail:
### 1. List:

#To print items in list using for loop:

this_list = ["A", "B", "C"]
for x in this_list:   #don't forget indentation in python codes 
    print(x)

#To check if item is present in the list:

this_list = ["A", "B", "C"]
if "D" in this_list :
    print("present")

#Note: You may add print statements to view your results.

#Use the append() to append an item in the list:

this_list = ["A", "B", "C"]
this_list.append("D")

#To insert item at a specified index in the list:

this_list = ["A", "B", "C"]
this_list.insert(1, "D")

#To remove a specific item from the list:

this_list = ["A", "B", "C"]
this_list.remove("B")

#To pop last item from the list:

this_list = ["A", "B", "C"]
this_list.pop()

#To removes an item from a specified index

this_list = ["A", "B", "C"]
del this_list[1]

#To clear the entire list

this_list = ["A", "B", "C"]
this_list .clear()

#To find length of the entire list

this_list = ["A", "B", "C"]
len(this_list)

#To join two lists

this_list = ["A", "B", "C"]
another_list = ["D", 3, 4]
result_list = this_list + another_list 

#result_list would have elements from both list

#To convert List to Tuple:

this_list = ["A", "B", "C"]
tuple(this_list )

#To slice List:

this_list = ["A", "B", "C"]
this_list[3:8]  #slicing the list

### 2. Tuple:

#To print items in Tuple:

this_tuple = ("A", "B", "C")
for x in this_tuple:
    print(x)

#To find length of Tuple:

this_tuple = ("A", "B", "C")
print(len(this_tuple))

#Convert

this_tuple = ("A", "B", "C")
list(this_tuple) #converting tuple to list

#To find type of Tuple:

this_tuple = ("A", "B", "C")
print(type(this_tuple))

#To slice Tuples 

this_tuple = ("A", "B", "C", "D" , "E")
print(this_tuple[1:]) #to print items from index 1 


#to print items starting from index 2 to index 3 (i.e 4-1)

print(this_tuple[2:4]) 
print(this_tuple[::-1]) #to print in reverse manner

#To delete a tuple 

this_tuple = ("A", "B", "C")
del this_tuple

### 3. Set:

#To print items in Set:

this_set = {"A", "B", "C"}
for x in thisset:
    print(x)

#To add items in set :

this_set = {"A", "B", "C"}
this_set .add("D")

#To update set :

this_set = {"A", "B", "C"}
this_set .update([1,2,3])

#To remove an item from a set:

this_set = {"A", "B", "C"}
this_set .remove("C")

#To pop item from set

this_set = {"A", "B", "C"}
this_set .pop()

#To clear everything from the set: 

this_set = {"A", "B", "C"}
this_set.clear()

#To add items form one set to another

this_set = {"A", "B", "C"}
another_set= {1, 2, 3}
this_set.update(another_set)


#Note: every time you run the command the items would be 
#Shuffled which justify that items in set are unordered.

#Operations in Sets: 

this_set = {1,2,3,4,5}
another_set= {3,4,5,6,7}

print(this_set|another_set) #Union
print(this_set - another_set) #Difference
print(this_set & another_set) #Intersection

### 4. Dictionary:

#To print a Dictionary: 
#items are in key:value pairs

this_dict = {
  "Name": "Suraj",
  "Age": "18",
  "Year": 2020
}
print(this_dict) #You can also use a for loop.

#Adding new index key with value: 

this_dict = {"Name": "Suraj",  "Age": "18",  "Year": 2020}
this_dict["newItem"] = "newValue"

#To pop a value from a dictionary: 

this_dict.pop("Year") #specifying key value 

#To clear the Dictionary:

this_dict.clear()

#To copy items from one Dictionary to another : 

this_dict = {"Name": "Suraj",  "Age": "18",  "Year": 2020}
another_dict = this_dict.copy()

#then print 

#To delete a value from Dictionary:

this_dict = {"Name": "Suraj",  "Age": "18",  "Year": 2020}
del Dict["Age"]

## Characters in Python :

character = "Hello World!"
print(character[1]) #to get character at index 1 
print(character[3:7]) #to get character at from index 3 to 6 
#It can also be done using negative indexes

#To find the length of the character
len(character)

#Some other basic functions:
character = "Hello World!"
print(character.lower()) #to convert to lowercase
print(character.upper()) #to convert to uppercase
print(character.replace("W", "Y")) #To replace characters in it
print(character.split(",")) #returns ['Hello World!']

## Logical operators in Python:

They are used to combine conditional statements.

* `and`: returns True if both statements are true .
* `or`: returns True if one of the statements is true .
* `not`: reverses the result, returns False if the result is true .

## Loops in Python:

#For loop
num = 0 
for num in range(0, 10): 
    print(num) #to print numbers from the range

#While loop
while (num < 10):     
    num = num + 1
    print(num) #to print numbers

If-else statements in Python:

num = 0 
for num in range(0, 10): 
    if(num<5):
        print(num) #to print numbers less than 5

## Functions in Python:

def function(x):
    print("Function called")
    print("Value passed is ",x)

function(5)