Industrial Training




For

Python For Loops


A for loop is used for iterating over a sequence (that is either a list, a tuple, a dictionary, a set, or a string).


This is less like the for keyword in other programming languages, and works more like an iterator method as found in other object-orientated programming languages.


With the for loop we can execute a set of statements, once for each item in a list, tuple, set etc.


Example


Print each fruit in a fruit list:


fruits = ["apple", "banana", "cherry"]
for x in fruits:
  print(x)

The for loop does not require an indexing variable to set beforehand.


Looping Through a String


Even strings are iterable objects, they contain a sequence of characters:


Example


Loop through the letters in the word "banana":


for x in "banana":
  print(x)

The break Statement


With the break statement we can stop the loop before it has looped through all the items:


Example


Exit the loop when x is "banana":

fruits = ["apple", "banana", "cherry"]
for x in fruits:
  print(x)
  if x == "banana":
    break

Example


Exit the loop when x is "banana", but this time the break comes before the print:

fruits = ["apple", "banana", "cherry"]
for x in fruits:
  if x == "banana":
    break
  print(x)

The continue Statement


With the continue statement we can stop the current iteration of the loop, and continue with the next:


Example


Do not print banana:


fruits = ["apple", "banana", "cherry"]
for x in fruits:
  if x == "banana":
    continue
  print(x)

The range() Function


To loop through a set of code a specified number of times, we can use the range() function,


The range() function returns a sequence of numbers, starting from 0 by default, and increments by 1 (by default), and ends at a specified number.


Example


Using the range() function:


for x in range(6):
  print(x)

Note that range(6) is not the values of 0 to 6, but the values 0 to 5.


The range() function defaults to 0 as a starting value, however it is possible to specify the starting value by adding a parameter: range(2, 6), which means values from 2 to 6 (but not including 6):


Example


Using the start parameter:


for x in range(2, 6):
  print(x)

The range() function defaults to increment the sequence by 1, however it is possible to specify the increment value by adding a third parameter: range(2, 30, 3):


Example


Increment the sequence with 3 (default is 1):


for x in range(2, 30, 3):
  print(x)

Else in For Loop


The else keyword in a for loop specifies a block of code to be executed when the loop is finished:


Example


Print all numbers from 0 to 5, and print a message when the loop has ended:


for x in range(6):
  print(x)
else:
  print("Finally finished!")

Nested Loops


A nested loop is a loop inside a loop.


The "inner loop" will be executed one time for each iteration of the "outer loop":


Example


Print each adjective for every fruit:


adj = ["red", "big", "tasty"]
fruits = ["apple", "banana", "cherry"]

for x in adj:
  for y in fruits:
    print(x, y)

The pass Statement


for loops cannot be empty, but if you for some reason have a for loop with no content, put in the pass statement to avoid getting an error.


Example

for x in [0, 1, 2]:
  pass



Hi I am Pluto.