Skip to main content

variables

· 6 min read
Shaurya Singhal

Source: View original notebook on GitHub

Category: Python / 1 Learn Python

variables

a=10
b=20
a

Output:

10
b

Output:

20

to see list of variables created

%whos

Output:

Variable   Type    Data/Info
----------------------------
a          int     10
b          int     20
li         list    n=6
li2        list    n=4
li3        list    n=8

list

li  = [1,2,3]

operations

  • append
  • remove
  • insert
  • pop
  • extend
  • index
  • sort
  • count
  • clear
  • reverse
li.append(12)
li

Output:

[1, 2, 3, 12]
li.append([1,2,3])
li

Output:

[1, 2, 3, 12, [1, 2, 3]]
li.extend([6,7,8])
li

Output:

[1, 2, 3, 12, [1, 2, 3], 6, 7, 8]
li.insert(3, 'shaurya')
li

Output:

[1, 2, 3, 'shaurya', 12, [1, 2, 3], 6, 7, 8]
li.insert(100,'last')
li

Output:

[1, 2, 3, 'shaurya', 12, [1, 2, 3], 6, 7, 8, 'last']
li.remove(2) # remove first presecnce of 2, result in error
#  if not found
li

Output:

[1, 3, 'shaurya', 12, [1, 2, 3], 6, 7, 8, 'last']
li.remove(2)

Output:

ValueError: list.remove(x): x not in list
li.pop() #remove last

Output:

'last'
li

Output:

[1, 3, 'shaurya', 12, [1, 2, 3], 6, 7, 8]
li.pop(3) # index should be in range else error

Output:

12
li

Output:

[1, 3, 'shaurya', [1, 2, 3], 6, 7, 8]

looping over list

li = [1, 3, 'shaurya', [1, 2, 3], 6, 7, 8]
for x in range(len(li)):
    print(li[x])

Output:

1
3
shaurya
[1, 2, 3]
6
7
8
for el in li:
    print(el)

Output:

1
3
shaurya
[1, 2, 3]
6
7
8
for el in li[2:]:
    print(el)

Output:

shaurya
[1, 2, 3]
6
7
8

Inputting a list

# 1. line seperated 
# 4
#1 
#2 
#3 
#4 

n =  int(input())
li = []
for i in range(n):
    li.append(int(input()))

Output:

4
1
2
3
4
li

Output:

[1, 2, 3, 4]
# 2. space seperated 
# 4
#1 2 3 4 
n = int(input())
li = [int(x) for x in input().split()]

Output:

5
5 6 7 8 9
li

Output:

[5, 6, 7, 8, 9]

Linear Search

# Linear Search
li = [21,82,33,47,54,66,79]
element_to_search = int(input())

for ele in li:
    if ele == element_to_search:
        print('---wollla--')
        break
else: #else works only if for loop executes completely 
        # not breaked by break    
    print(-1)

Output:

47
---wollla--

passing list to function

def changelist(li):
    li[0] = 'shaurya'  
li = [3,4,6,7]
changelist(li)
li

Output:

['shaurya', 4, 6, 7]

reversing list

li = [3,4,5,87,7,8,7,9,0]
length = len(li)
for ele in range(length//2):
    li[ele] ,li[length-1-ele] = li[length-1-ele],li[ele]
    
li

Output:

[0, 9, 7, 8, 7, 87, 5, 4, 3]
li = [3,4,5,87,7,8,7,9,0]
li[::-1] # if using -ve step ,starts become -1
            # and end reaches before 0
    
    # or if -ve step
    # swap end and start ad shift by one position to left!!

Output:

[0, 9, 7, 8, 7, 87, 5, 4, 3]
li = [0, 9, 7, 8, 7, 87, 5, 4, 3]
for ele in range(len(li)//2):
    li[ele] ,li[-1-ele] = li[-1-ele],li[ele]
    
li

Output:

[3, 4, 5, 87, 7, 8, 7, 9, 0]

strings

  • sequence of characters stroed as unicode values internally
string =  'shaurya singhal'
string[8:2:-1]

Output:

's ayru'

List comprehension

li = [ele**2 for ele in range(10)]
li

Output:

[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
# with condition

li =  [ele**2 for ele in range(10) if ele%2==0]
li

Output:

[0, 4, 16, 36, 64]
# with nested condition

for ele in range(20):
    if ele%3==0:
        if ele%2==0:
            print(ele,end =' ')

Output:

0 6 12 18
li = [ele for ele in range(20) if ele%3==0 if ele%2==0]
li

Output:

[0, 6, 12, 18]
# nested forloops

li = [ele+2*ele2 for ele in range(5) for ele2 in range(5) ]
li

Output:

[0, 2, 4, 6, 8, 1, 3, 5, 7, 9, 2, 4, 6, 8, 10, 3, 5, 7, 9, 11, 4, 6, 8, 10, 12]
# nested forloops with condition

li = [ele+2*ele2 for ele in range(5) for ele2 in range(5) \
      if (ele+2*ele2)%2==0]
li

Output:

[0, 2, 4, 6, 8, 2, 4, 6, 8, 10, 4, 6, 8, 10, 12]
# input a 2d list

# n,m
# n-m elements in n lines

size = input().split()
n,m = int(size[0]),int(size[1])

li = [[int(j) for j in input().split()] for i in range(n)]

Output:

3 4 
1 2 3
1 2 4 5
12 3 4  5 45 6 765 7
li

Output:

[[1, 2, 3], [1, 2, 4, 5], [12, 3, 4, 5, 45, 6, 765, 7]]

tuples

a,n = 2,3
type((a,n))

Output:

tuple
t = (1,2,3,4,5)
t

Output:

(1, 2, 3, 4, 5)
a = 1,2,3
b = 4,5,6
c = (a,b)
c = c*4
c.count((4))

Output:

0

dict

  • fromkeys()
  • copy
  • count
  • get
  • setdefault()
  • items
  • values
  • keys
d = dict([('shaurya',3),(4,7),(234,67)])
d

Output:

{'shaurya': 3, 4: 7, 234: 67}
len(d)

Output:

3
min(d)

Output:

TypeError: '<' not supported between instances of 'int' and 'str'