Python for loop

In this python article, we will discuss how to iterate using the for loop with some examples.

1. for loop

for loop is iteration statements, which allow a set of instructions to be performed repeatedly until a certain condition is fulfilled. Basically, we use it to iterate over elements from a list, string, dictionary etc.

for loop flowchart

As soon as we reach the last element it will skip the statement block and jump to the next statement.

Syntax: 
for variable_name in iterable:
  Statement-sequence

2. range() function

range() function is an in-built function in Python that is used to return a sequence of numbers.

Syntax:
range(start , end , increment)

Default values of start and increment are 0 and 1 respectively.

So if we use range(5) – our loop will run for values 0, 1, 2, 3, 4

  • Start(optional) defined the point, we want to start our sequence, by default 0
  • End (Required) defines the last value of the sequence
  • Increment (optional) defined how many steps or count we want to go at a time, by default 1
x = 12
for i in range(2, x, 2):
  print(i)
Output
2
4
6
8
10

Let’s see how we can access element from different iterators using for loop.


3. Looping through a list

We can access list element using loop through two ways:

  • using range function and access the element of the list via index
  • without using the range function and directly access the elements
x = [1, 2, 3, 4, 5, 7]

#using range() function
for i in range(len(x)):
  print(x[i], end=", ")

print("")

#without using range() function
for i in x:
  print(i,  end=", ")
Output
1, 2, 3, 4, 5, 7, 
1, 2, 3, 4, 5, 7,

4. Looping through a string

Similar to the ways we access the list, we can access string elements using for loop.

x = "Codingeek"

#using range() function
for i in range(len(x)):
  print(x[i], end=", ")

print("")

#without using range() function
for i in x:
  print(i,  end=", ")
Output
C, o, d, i, n, g, e, e, k, 
C, o, d, i, n, g, e, e, k,

5. Break Statement

Sometimes we do not need to loop through all the elements, so if we want to break the loop in-between then for that we use break keyword.

In the below example as soon as it counters the value of sum greater than 7 it will break the loop

sum = 0
for i in range(10):
    if sum > 7:
        break
    sum += i
    print(sum)
Output
0
1
3
6
10

6. Continue statement

When we want to skip some part of the for loop just for that specific iteration and jump to the next iteration then we use the continue keyword.

In the below example as soon as it counters the value 5 then it will not print it and go to the next loop.

for i in range(7):
    if i == 2:
        continue
    print(i)
Output
0
1
3
4
5
6

7. Pass statement

We can’t write an empty for loop so instead of keeping it empty we write a pass keyword in it.

for i in range(5):
    pass

8. loop with else statements

Sometimes we want to do something only if the for loop finishes without breaking in between then we use else keyword.

This else block will execute only if the loop runs completely without a break.

x = [1, 2, 3, 4]

for i in x:
    print(i)
else:
    print("Codingeek")

# breaking the loop in-between
# else block will not run
for i in x:
    if i > 2:
        break
    print(i)
else:
    print("Codingeek")
Output
1
2
3
4
Codingeek
1
2

9. Conclusion

In this article we learned about

  • for loop
  • break statement
  • continue statement
  • pass statement
  • for loop with else block

Helpful Links

Please follow the Python tutorial series or the menu in the sidebar for the complete tutorial series.

Complete code samples are present on Github project.

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An investment in knowledge always pays the best interest. I hope you like the tutorial. Do come back for more because learning paves way for a better understanding

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Happy coding!! 😊

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