Printing dynamic ascii-art shapes based on user input

Question

In the following code I used a while True: loop and implemented break, because I couldn't figure out a cleaner solution than an infinite loop. Is this approach considered bad practice? Here is my code:

while True:
    z = int(input("Y: "))

    if (z >= 0 and z <= 20):
        break

for x in range(z):

    print("-" * (z-x) + "*" * x + " " * x + "-" * (z-x))

... which outputs:

Y: 12
------------------------
-----------* -----------
----------**  ----------
---------***   ---------
--------****    --------
-------*****     -------
------******      ------
-----*******       -----
----********        ----
---*********         ---
--**********          --
-***********           -

Answer 1

I couldn't figure out a cleaner solution than an infinite loop. Is this approach considered bad practice?

You can't do much better, since Python doesn't have the equivalent of a C-style do/while.

This is a trivial program so I doubt it's even worth adding functions (etc.); the one thing that can be improved is

if (z >= 0 and z <= 20):

can be

if 0 <= z <= 20:

Answer 2

I thought I'd add a useful concept for more complex cases. I fully agree with the previous answers though, they are more adequate for a simple case like this.

The walrus operator := can be useful when looping and simultaneously updating a variable. So in your simple case it might look like this:

while (z := int(input("Y: "))) not in range(0, 21):
    pass

An equivalent way to write it would be

while not (0 <= (z := int(input("Y: "))) <= 20):
    pass

This will assign int(input("Y: ")) to z until it is in range(0, 21), i.e. between 0 and 21. This makes it so you could use z for further calculations in the body of your loop without the need for additional assignment. This will throw an error for non-number inputs though, so be careful. I personally only prefer this approach if there are additional calculations to be done with the value, since I don't like using pass here. I find it actually decreases readability compared to your approach.

Answer 3

There's nothing wrong with using a while True loop: it often produces the most readable implementation.

Here's an alternative approach. It has one clear benefit: it handles invalid inputs. It also illustrates a useful technique to include in the toolbox: recursion for user-input, validation, and related needs that can fail but tend not to fail a large N of times. Opinions often differ on such matters, but this one reads about as well to me as the while True loop. Finally, when checking whether an integer falls within certain bounds, a range() is sometimes clearer than a pair of comparisons (and it does not raise a TypeError if the value is None).

def get_int(prompt):
    try:
        z = int(input(prompt))
    except ValueError:
        z = None
    return z if z in range(0, 21) else get_int(prompt)