Syntax and Examples

Introduction to For Loops

Syntax and Examples

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Python For Loop Syntax

How to write a for loop

A couple of important reminders:

  • Every for loop must start the same way (shown below)
  • Everything inside the for loop must be indented

The basic formula for a for loop in python is below:

  • for thing in iterable:

You replace the word thing with whatever you want to call each element in your iterable. This is a variable that you come up with, so its name does not matter. It is important though that you make sure you pass in the correct iterable and therefore the name for the iterable does matter.

For example if you had a list called lst that contained a couple of numbers, I would set up my for loop with the following:

  • for number in lst:

For Loop List Example

Below is an example of this in action, where we iterate through a list of numbers and print out each one:

            
# Create the list lst = [1,2,3,4,5,6] # Create the for loop for number in lst: # Create print statement print(number)

For Loop Set Example

Here is another example but instead of using a list, we are using a set

            
# Create the set st = {1,2,3,4,5,6} # Create the for loop for number in st: # Create print statement print(number)

For Loop Dictionary Items Example

Here is an example of iterating through all the items in a dictionary. To iterate through just the keys, we would use .keys() and similarly, to iterate through all of the values we would use .values()

            
# Create the dictionary d = {'a':1,'b':2,'c':3} # Create the for loop for item in d.items(): # Create print statement print(item)

For Loop with Letters in a String

Here we are going to go through all the letters in a string. This is different than iterating though all the words in a string. You should be able to test this out in the IDE. The following example will be looping through words.

            
# Create the dictionary string = 'Hello World, How are you' # Create the for loop for character in string: # Create print statement print(character)

For Loop with Words in a String

To iterate through a bunch of words, we need to split our string on each space. The command to do this is string.split(' ') where we are using the space character to split.

            
# Create the dictionary string = 'Hello World, How are you' print(string.split(' ')) # Create the for loop for word in string.split(' '): # Create print statement print(word)
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