if statement can be used to execute code conditionally. That means only if an expression is true.
Let’s take a look at some expressions first
3 > 4
a = 3 b = 4 a > b
a < b
# not equal a != b
# equal a == b
# Note: Do not mix it up with this: a = b
if in combination with an expression, you need to put a colon
: and following code must be indented:
if 3 < 4: print("Math is great.")
Math is great.
if 3 > 4: print("Math is weird.")
You can also write more sophisticated comparisons:
c = 10 if 4 < c < 20: print("C is between 4 and 20.")
C is between 4 and 20.
Or combine expressions using
if c > 4 and c < 10: print("C is between 4 and 20.")
If you want to check if an element is in an array, do it like this:
animals = ['cat', 'dog', 'mouse'] if 'cat' in animals: print('Our list of animals contains a cat')
Our list of animals contains a cat
You can also analyse strings. For example check if they start or end with certain characters:
filename = "cells.tif" if filename.endswith("tif"): print("The file is an image!")
The file is an image!
If you have two different pieces of code that should be executed alternatively, use
quality_in_percent = 89 if quality_in_percent > 90: print("Our quality is high enough.") else: print("We need to improve our quality.")
We need to improve our quality.
For executing code depending on multiple conditions, use the
# determining the exam grade depending on number_of_correct_points = 23 number_of_total_points = 30 # compute percentage percentage = number_of_correct_points / number_of_total_points * 100 if percentage > 95: grade = 1 elif percentage > 80: grade = 2 elif percentage > 60: grade = 3 elif percentag > 50: grade = 4 else: grade = 5 print("You scored", number_of_correct_points, "out of", number_of_total_points) print("Your grade is", grade)
You scored 23 out of 30 Your grade is 3
Write python code that prints out the daytime, e.g. “morning”, “noon”, “afternoon”, “evening” and “night” depending on a given time.
# it's 12:15 time_hours = 12 time_minutes = 15