Python for loop

In the Python programming language, the for loop is often used to repeat code. Another word for "repeat code" is iteration.

Other than iterating over code, a for loop can iterate any sequence of items, such as a list or a string.

grammar:

for loop syntax is as follows:

   for iterating_var in sequence:
       statements (s)

flow chart:

The control flow graph shows the execution of a for loop

Example:

#!/usr/bin/python
#-*- coding: UTF-8 -*-

for letter in 'Python': # first instance
   print('current letter:', letter)

fruits = [ 'banana', 'apple', 'mango']
for fruit in fruits: # second instance
   print('current letter:', fruit)

print("Good bye!")

Examples of the above output:

current letter: P
current letter: y
current letter: t
current letter: h
current letter: o
current letter: n
current letter: banana
current letter: apple
current letter: mango

by an iterative sequence index

You can traverse through the execution cycle by index, the following examples:

#!/usr/bin/python
#-*- coding: UTF-8 -*-

fruits = [ 'banana', 'apple', 'mango']
for index in range(len(fruits)):
    print("Current fruit:", fruits[index])

print("Good bye!")

Examples of the above output:

Current fruit: banana
Current fruit: apple
Current fruit: mango
Good bye!

The above examples we use the built len() function and range(), len() function returns the length of the list, i.e. the number of elements. range returns a sequence number.

Other examples

Print a triangular array 1-9:

#!/usr/bin/python
# - * - coding: UTF-8 - * -

for i in range (1,11):
    for k in range (1, i):
        print(k, end=''),
    print("\n", end='')

Example of the above output:

1
12
123
1234
12345
123456
1234567
12345678
123456789

You can also use a for loop on a dictionary, but this works a bit differently:

d = {'x': 1, 'y': 2, 'z': 3} 
for k,v in d.items():
    print(k, 'corresponds to', v)