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Python - For Loop

What is a for Loop?

If we want to execute a group of statements for every element present in a sequence, we use the for loop.

A sequence can be a string, list, tuple, set, range, or dictionary.

Syntax of for Loop

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Another Syntax

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Flow of for Loop

  1. Take the first element from the sequence.
  2. Execute the loop body.
  3. Take the next element.
  4. Repeat until all elements are processed.
  5. When there are no more elements, the loop stops.

range() Function

The range() function is used to generate a sequence of numbers.

It returns a range object.

Three Forms of range()

Form Description
range(n) Generates numbers from 0 to n-1.
range(begin, end) Generates numbers from begin to end-1.
range(begin, end, step) Generates numbers using the specified step value.

Form 1 - range(n)

This form generates numbers from 0 to n-1.

Example 1 - Print Numbers from 0 to 9

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0
1
2
3
4
5
6
7
8
9

Explanation

range(10) generates numbers from 0 to 9.

The value 10 is not included.

Example 2 - Print "Hello" 5 Times

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Hello
Hello
Hello
Hello
Hello

Form 2 - range(begin, end)

This form generates numbers from begin to end-1.

Example 1 - Print Numbers from 10 to 20

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10
11
12
13
14
15
16
17
18
19
20

Explanation

The starting value is included.

The ending value is excluded.

Therefore, range(10, 21) prints numbers from 10 to 20.

Example 2 - Print Numbers from 1 to 10

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1
2
3
4
5
6
7
8
9
10

Example 3 - Print Numbers from 5 to 10

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5
6
7
8
9
10

Form 3 - range(begin, end, step)

The third argument specifies the increment or decrement.

Example 1 - Print Even Numbers

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0
2
4
6
8
10
12
14
16
18
20

Explanation

The value increases by 2 after every iteration.

Only even numbers are printed.

Example 2 - Print Odd Numbers

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1
3
5
7
9
11
13
15
17
19

Example 3 - Print Numbers from 10 to 1

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10
9
8
7
6
5
4
3
2
1

Explanation

A negative step decreases the value after every iteration.

This prints the numbers in reverse order.

Example 4 - Print Even Numbers in Reverse

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20
18
16
14
12
10
8
6
4
2

Example 5 - Print Numbers from 10 to 0

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10
9
8
7
6
5
4
3
2
1
0

Important Notes about range()

Form Description
range(n) Generates numbers from 0 to n-1.
range(begin, end) Generates numbers from begin to end-1.
range(begin, end, step) Generates numbers using the specified step value.

Summary of range()

Function Output
range(5) 0 1 2 3 4
range(1, 6) 1 2 3 4 5
range(0, 11, 2) 0 2 4 6 8 10
range(10, 0, -1) 10 9 8 7 6 5 4 3 2 1

Important Points

  • The for loop is used to iterate over a sequence.
  • The range() function returns a range object.
  • range(n) generates numbers from 0 to n-1.
  • range(begin, end) generates numbers from begin to end-1.
  • range(begin, end, step) allows custom increment or decrement.
  • A negative step generates numbers in reverse order.

Quick Summary

Topic Description
for Loop Iterates over each element of a sequence.
range(n) 0 to n-1
range(begin, end) begin to end-1
range(begin, end, step) Uses a custom step value.

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