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Use for Loop That Loops Over a Sequence in Python

Last Updated : 24 Feb, 2023

In this article, we are going to discuss how for loop is used to iterate over a sequence in Python.

Python programming is very simple as it provides various methods and keywords that help programmers to implement the logic of code in fewer lines. Using for loop we can iterate a sequence of elements over an iterable like a tuple, list, dictionary, set, String, etc. A sequence consists of multiple items and this item can be iterated using in keyword and range keyword in for loop.

Syntax of for loop:

for variable in Sequence:

    #....code...

Syntax of range method

• range(a) -> Generates a sequence of items from 0^th index to a-1 index. 
• range(a, b) -> Generates a sequence of items from a^th index to b-1 index. 
• range(a, b, step) -> Generates a sequence started from a, end at b-1 and c is difference.

Note: Range method is not used when any type of sequence won't support indexing.

A list is used to store the multiple values of the different types under a single variable. It is mutable i.e., items in the list can be changed after creation. The list is created by enclosing the data items with square brackets.

# list creation
li = ["Geeks", "for", "Geeks"]

for i in li:
    print(i)
print('-----')
for i in range(len(li)):
    print(li[i])

Geeks
for
Geeks
-----
Geeks
for
Geeks

Time complexity: O(n) where n is the length of the list.
Auxiliary space: O(1) as no extra space is used.

A tuple is used to store the multiple values of the different types under a single variable. It is immutable i.e., items in a tuple cannot be changed after creation. A tuple is created by enclosing the data items with round brackets.

# tuple creation
seq = ("Geeks", "for", "Geeks", 
       "GFG", "Learning", "Portal")

for i in seq:
    print(i)
print('-----')
for i in range(3, len(seq)):
    print(seq[i])

Geeks
for
Geeks
GFG
Learning
Portal
-----
GFG
Learning
Portal

Time complexity: O(n), where n is the length of the tuple.
Auxiliary space: O(1), as we are not using any additional data structure to store the elements of the tuple.

Dictionary is an unordered collection of items where data is stored in key-value pairs. Unlike other data types like list, set and tuple it holds data as key: value pair. for loop uses in keyword to iterate over each value in a dictionary.

# dictionary creation
dic = {1: "a", 2: "b", 3: "c", 4: "d"}

for i in dic:
    print(i)

A set is an unordered, unindexed, and immutable datatype that holds multiple values under a single variable. It can be created by surrounding the data items around flower braces or a set method. As the set is unindexed range method is not used.

# set creation
setSeq = {"unordered", "unindexed", "immutable"}

for i in setSeq:
    print(i)

unordered
unindexed
immutable

Here we passed the step variable as 2 in the range method. So we got alternate characters in a string.

# string creation
str = "GFG Learning-Portal"

for i in str:
    print(i, end="")

print()
for i in range(0, len(str), 2):
    print(str[i], end="_")

GFG Learning-Portal
G_G_L_a_n_n_-_o_t_l_

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