Stacks: Python
Stacks Python Size II

It’s time to add a couple helper methods.

Helper methods simplify the code we’ve written by abstracting and labeling chunks of code into a new function. Here’s an example:

# Adding "!" without a helper saying = "I love helper methods" exclamation = saying + "!" # Adding "!" with a helper def add_exclamation_to_string(str): return str + "!" exclamation2 = add_exclamation_to_string("I love helper methods")

This might seem like a silly example, but think about the benefit of the add_exclamation_to_string helper.

  1. The name tells us what this function does.
    • Without a helper, we need to read the code to understand its meaning.
  2. The function lets us repeat this behavior
    • Without a helper, we’d need to rewrite the same code!

First, we want one that checks if our stack has room for more items. We can use this in push() to guard against pushing items to our stack when it’s full.

Second, it’s helpful to have a method that checks if the stack is empty…



Define a new method has_space() in Stack. The method should return True if self.limit is greater than self.size.


Go back to your push() method — we need to make sure we’re keeping track of our stack size when we add new items. At the end of your method body, increment self.size by 1.


Now add an if clause at the top of push() that checks if your stack has space (using your newly created helper method).

  • If there’s space, the rest of the body of the method should execute
  • If there’s no space, we want to print a message letting users know that the stack is already full. Something like “All out of space!” should be good.

Finally, let’s define a new method is_empty() in Stack.

The method should return True if the stack’s size is 0.

Anywhere we’ve written if self.size > 0: can now be replaced with if not self.is_empty().

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