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Loops

Loops provide a means to perform the same action across multiple items. Multiple items are typically stored in a Python list object. Any list-like object can be iterated over (e.g., tuples, arrays, dataframes, dictionaries). More information on loops can be found in the Software-Carpentry Python lesson on loops.¹

1. https://swcarpentry.github.io/python-novice-inflammation/05-loop/index.html

To loop over a list. we use a for statement. The basic for loop looks like this:

for item in container:
  # do something

The container represents some iterable set of values (e.g., a list). The item represents a temporary variable that represents each item in the iterable. In the for statement, the first element of the container is assigned to the temporary variable (in this example, item). Everything in the indented block after the colon is then performed. When it gets to the end of the loop, the code assigns the next element in the iterable to the temporary variable and performs the steps over again.

Click here to view code image

# an example list of values to iterate over
l = [1, 2, 3]

# write a for loop that prints the value and its squared value
for i in l:
  # print the current value
  print(f"the current value is: {i}")

  # print the square of the value
  print(f"its squared value is: {i*i}")

  # end of the loop, the 
 at the end creates a new line
  print("end of loop, going back to the top
")

the current value is: 1
its squared value is: 1
end of loop, going back to the top

the current value is: 2
its squared value is: 4
end of loop, going back to the top

the current value is: 3
its squared value is: 9
end of loop, going back to the top