Python Loops: For and While

Python has two primitive loop commands: while loops and for loops.

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

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

[!NOTE] Remember to increment i, or else the loop will continue forever!

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

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

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

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

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

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

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

| Function | Result | | :--- | :--- | | range(6) | Values from 0 to 5 | | range(2, 6) | Values from 2 to 5 | | range(2, 30, 3) | Values from 2 to 29, incrementing by 3 |

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

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

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

[!IMPORTANT] The else block will not be executed if the loop is stopped by a break statement.

4. 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".

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

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

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.

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