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Python Loops

Python has two primitive loop commands:

  • while loops
  • for loops

The while Loop​

With the while loop, we can execute a set of statements as long as a condition is true.

Example​

i = 1
while i < 6:
  print(i)
  i += 1

The while loop requires relevant variables to be ready, in this example we need to define an indexing variable, i, which we set to 1.

The break Statement​

With the break statement, we can stop the loop even if the while condition is true.

Example​

i = 1
while i < 6:
  print(i)
  if i == 3:
    break
  i += 1

The continue Statement​

With the continue statement, we can stop the current iteration and continue with the next.

Example​

i = 0
while i < 6:
  i += 1
  if i == 3:
    continue
  print(i)

The else Statement​

With the else statement, we can run a block of code once when the condition no longer is true.

Example​

i = 1
while i < 6:
  print(i)
  i += 1
else:
  print("i is no longer less than 6")

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).

Example​

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

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

Looping Through a String​

Even strings are iterable objects; they contain a sequence of characters.

Example​

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​

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

The continue Statement​

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

Example​

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​

for x in range(6):
  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​

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

Nested Loops​

A nested loop is a loop inside a loop.

nested loop

Example​

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

This documentation covers the basics of Python loops, including while and for loops, along with control flow statements like break, continue, and else. Examples are provided for each concept to illustrate their usage effectively.