Day 4

PS: These are notes, there could be grammar error and spelling errors.

for loops

For loop over a list goes as follows:

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>>> a = ['Fedora', 'is', 'powerful']
>>> for x in a:
...    print(x)
...
# these ... are automatically created by python interpreter
Fedora
is
powerful

range() function

range function creates lists based on parameter passed in function``py

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>>> list(range(1, 5)) # when two numbers are passed n,j List starts at n ends at j-1
 [1, 2, 3, 4]
>>> list(range(1, 15, 3)) # when three numbers are passed n,j,k. List starts at n ends at j after stepping at every k steps
[1, 4, 7, 10, 13]
>>> list(range(10)) # when only single number n is passed list starts from 0 and ends after n elements
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Continue statement

Just like break is use to break loop, continue is used to continue loop towards iteration without further execution A combined example.

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#!/usr/bin/env python3
while True:
    n = int(input("Please enter an Integer: "))
    if n < 0:
        continue # this will take the execution back to the starting of the loop
    elif n == 0:
        break
    print("Square is ", n ** 2)
print("Goodbye")

Data Structures

Lists

Few other things with lists:

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# to insert a new element in list
>>> a = [23, 45, 1, -3434, 43624356, 234]
>>> a.append(45)
>>> a
[23, 45, 1, -3434, 43624356, 234, 45]
# to inset at particular position we have to pass position along. First would be position then would be element
>>> a.insert(0, 1) 
>>> a
[1, 23, 45, 1, -3434, 43624356, 234, 45]
# to count number of occurrences of a element
>>> a.count(45)

Same way we have .reverse, .remove using append we can append another list to existing list as a element of the list

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>>> b = [45, 56, 90]
>>> a.append(b)
>>> a
[45, 43624356, -3434, 1, 45, 23, 1, 111, [45, 56, 90]]

There is another method call .extend which would add element of second list as element of new list

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>>> a.extend(b) #To add the values of b not the b itself
>>> a
[45, 43624356, -3434, 1, 45, 23, 1, 111, [45, 56, 90], 45, 56, 90]
>>> a[-1] # here in a[n] value of n  is -1 so it would give last element
90
# to remove element which was we would pass same list or sublist to remove it.
>>> a.remove(b)
>>> a
[45, 43624356, -3434, 1, 45, 23, 1, 111, 45, 56, 90]
# .sort is use to sort list if list is sortable means elements are comparable.
# del can also be used to delete a element from list
>>> del a[-1]
>>> a
[-3434, 1, 1, 23, 45, 45, 45, 56, 90, 111]

Using lists as stack and queue

Stacks work as LIFO(Last In First Out) and queue work on FIFO(First In First Out)

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>>> a = [1, 2, 3, 4, 5, 6]
>>> a
[1, 2, 3, 4, 5, 6]
# for Lifo and fifo everything would be appended at the end of list we would use append.
>>> a.append(34)
>>> a
[1, 2, 3, 4, 5, 6, 34]
# while removing element we would remove using pop
# for removing element in lifo we would use .pop() without any parameter so that it would remove last element
>>> a.pop()
34
# for fifo or queue where oldest element is removed first we use .pop(0)
>>> a.pop(0)
1

Note: .pop removes element and return removed element while append just add element doesn’t returns anything