Python Projects for Beginners a ten-Week Bootcamp Approach to Python Programming

Generating a List of Numbers

Let’s try generating a list of numbers from 0 all the way up to 100 using list comprehension:

# create a list of ten numbers using list comprehension
nums = [ x for x in range(100) ] # generates a list from 0 up to 100 print(nums)

Go ahead and run the cell. You’ll notice that we output a list that includes 100 numbers. List comprehension has allowed us to build out this list within a single line rather than writing out the for loop and append statement on separate lines. The comprehension from the preceding cell is an exact representation of the following code:
>>> nums = [ ] >>> for x in range(100):
>>> nums.append(x)
As you can see, we’ve reduced three lines down to one using comprehension. This doesn’t improve performance but does reduce the number of lines within our code. It becomes more apparent in larger programs, and I highly recommend that you try to use comprehension when possible. Going forward we’ll begin to use list comprehension when building out lists.

If Statements

Earlier, we went over how the syntax changes when including an if statement in your comprehension. Let’s try an example by making a list of only even numbers:

# using if statements within list comprehesion
nums = [ x for x in range(10) if x % 2 == 0 ] # generates a list of even numbers up to 10
print(nums)

Go ahead and run the cell. For this comprehension, the variable x only gets appended to the list when the condition proves True. In our case, the condition is True when the current value of x is divisible by two. In the following, you’ll find the same code that is needed without using comprehension:
>>> nums = [ ] >>> for x in range(10):
>>> if x % 2 == 0:
>>> nums.append(x)
This time we were able to reduce four lines of code down to one. This can often improve readability of your code.