For Loop
for val in sequence:
# Body of for loop
Here,
val is the variable that takes the value of the element inside the sequence on each iteration.Loop continues until we reach the last item in the sequence. The body of for loop is separated from the rest of the code using indentation.
Flowchart of for Loop in Python
Flowchart of for Loop in Python programming
# Program to find the sum of all numbers stored in a list
# List of numbers
numbers = [6, 5, 3, 8, 4, 2, 5, 4, 11]
# variable to store the sum
sum = 0
# iterate over the list
for number in numbers:
sum = sum + number
print("The sum is", sum)
When you run the program, the output will be:
The sum is 48
We can generate a sequence of numbers using
range() function. range(10) will generate numbers from 0 to 9 (10 numbers).We can also define the start, stop and step size as
range(start, stop, step_size). step_size defaults to 1 if not provided.The
range object is "lazy" in a sense because it doesn't generate every number that it "contains" when we create it. However, it is not an iterator since it supports in, len and __getitem__ operations.This function does not store all the values in memory; it would be inefficient. So it remembers the start, stop, step size and generates the next number on the go.
To force this function to output all the items, we can use the function
list().The following example will clarify this.
print(range(10))
print(list(range(10)))
print(list(range(2, 8)))
print(list(range(2, 20, 3)))
Output
range(0, 10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[2, 3, 4, 5, 6, 7]
[2, 5, 8, 11, 14, 17]
We can use the
range() function in for loops to iterate through a sequence of numbers. It can be combined with the len() function to iterate through a sequence using indexing. Here is an example.# Program to iterate through a list using indexing
genre = ['pop', 'rock', 'jazz']
for g in genre:
print("I like", g)
# iterate over the list using index
for i in range(len(genre)):
print("I like", genre[i])
Output
I like pop
I like rock
I like jazz
A
for loop can have an optional else block as well. The else part is executed if the items in the sequence used in for loop exhausts.The
break keyword can be used to stop a for loop. In such cases, the else part is ignored.Hence, a for loop's else part runs if no break occurs.
Here is an example to illustrate this.
digits = [0, 1, 5]
for i in digits:
print(i)
else:
print("No elements left.")
When you run the program, the output will be:
0
1
5
No elements left.
Here, the for loop prints items of the list until the loop exhausts. When the for loop exhausts, it executes the block of code in the
else and prints No items left.This
for...else statement can be used with the break keyword to run the else block only when the break keyword was not executed. Let's take an example:# program to display people's ages from record
person_name = 'Daniel'
people = {'John': 45, 'Diana': 32, 'Artur': 90}
for person in people:
if person == person_name:
print(people[person])
break
else:
print('No entry with that name found.')
Output
No entry with that name found.
Last modified 2yr ago