Consider how the terms are used in common language: FOR For each day in July, I will practice writing loops. For every student in the class, provide a lunchtime meal. For each letter in the alphabet, write down a word beginning with that letter. For numbers in the range 1 to 10, calculate the square root. Notice that for each case, we iterate through multiple things (days in the month / students in the class / letters in the alphabet / numbers in a range). WHILE While there is still daylight, we can play football. While the music is playing, we will dance. While I am waiting, I will read a book. While my set of Pokémon cards is incomplete, I will keep collecting them. Notice that in each case, something is done for as long as a condition (a "predicate") is satisfied (is "True"). In these examples, the predicates are: "There is daylight?", "The music is playing?", "I am waiting?", "The set is incomplete?". As soon as the answer is "False", the loop stops. More on reddit.com

I've been writing Python scripts for a while now. Nothing crazy, just automating small stuff, scraping some data, making my life a little easier. I thought I had a decent handle on things. I was looking at someone else's code and they used a list comprehension in a way that made me stop and read it three times. I realized I had been writing loops ... More on reddit.com

If you want to modify a global from within a function scope you need to use global in the function (basically saying "use the upper scope instead of local"). Generally though try to avoid globals as good programming style.

Example demonstrating this:

global test

def set_true_local():
    test = True

def set_true_global():
    global test     # Use global version of test
    test = True

test = False
print('Before: {}'.format(test)) # False

set_true_local()
print('After set_true_local: {}'.format(test)) # False

set_true_global()
print('After set_true_global: {}'.format(test)) # True

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You have two variables, m and c. The variable m is what the user inputs to determine what height the ball is dropped from. The variable c will count the number of bounces.

Then the while loop starts. Quite literally, while the ball bounces back to a height that is greater than 0.01, your program keeps executing the rest of the code over and over.

In this specific case, your program first decreases the height to 70% of previous value (so it bounces back lower due to gravity), then increments the c counter by one, so says the ball bounces one time.

Then the instruction in the while loop is over. The program checks again if the height m is greater than 0.01. If it is, it will keep repeating the while loop code block until the condition is no longer met. If it isn't, it will do the rest of the code. In this example it will print that the ball has bounced c number of times.

You print c because that is the variable where you store number of bounces. If you printed m it would print the height the ball is at right now, after all those operations. Which would mean it would print a number that's less than 0.01.

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