Python For Loop
A for loop is used to execute a block of code repeatedly for a specific number of times or until some conditions are true.
A for loop is commonly used to iterate over items of list, tuple, dictionaries, sets, string letters, etc.
Example 1
A program to print a list of string items using for a for loop:
fruits = ["grapes", "mango", "apple", "pineapple", "banana"]
for i in fruits:
print(i)
Output
mango
apple
pineapple
banana
Example 2
Print numbers from 1 to 10:
for i in range(1, 11):
print(i)
Output
2
3
4
5
6
7
8
9
10
Example 3
Print negative numbers from -10 to -1:
start, end = -10, 0
for num in range(start, end):
if num < 0:
print(num, end = " ")
Output
The break statement
The break statement is used to terminate the loop before the looping through all items is complete.
Example
Terminate the loop when i is mango:
fruits = ["grapes", "mango", "apple", "pineapple", "banana"]
for i in fruits:
#exit loop when i is mango
if(i == "mango"):
break
print(i)
print("End of program")
Output
End of program
The continue statement
The continue statement is used to skip the current loop and continue with the next loop.
Example
Skip when i is "apple"
fruits = ["grapes", "mango", "apple", "pineapple", "banana"]
for i in fruits:
#go to next loop if the current value of i is apple
if(i == "apple"):
continue
print(i)
print("End of program")
Output
pineapple
banana
End of program
The pass statement
The for loop cannot iterate over an empty items. Therefore, to prevent error from happening in such cases, the pass statement is used.
Example
Iterate over an empty list:
fruits = []
for i in fruits:
pass
The range function
The range() function returns a sequence of numbers starting from 0. You can use the range() function with the for loop to repeatedly run a block of code a specified number of times.
Example
fruits = ["grapes", "mango", "apple", "pineapple", "banana"]
for i in range(5):
print(fruits[i])
Output
mango
apple
pineapple
banana
Nested for loop
The nested for loop is a loop within a loop. In a nested loop, the first pass of the outer loop triggers the inner loop, the inner loop executes to completion.
Example
x = ["a", "b", "c", "d", "e"]
y = [1, 2, 3, 4, 5]
for i in x:
for j in y:
print(i,j)
Output
a 2
a 3
a 4
a 5
b 1
b 2
b 3
b 4
b 5
c 1
c 2
c 3
c 4
The range function
The range() function returns a sequence of numbers starting from 0. You can use the range() function with the for loop to repeatedly run a block of code a specified number of times.
Example
fruits = ["grapes", "mango", "apple", "pineapple", "banana"]
for i in range(5):
print(fruits[i])
Output
mango
apple
pineapple
banana