Expressions

The third major building block of Python programs is expressions. We've seen expressions in every example so far because it's nearly impossible to do anything in Python without using expressions.

Expressions consist of data values and operations to perform on those data values. The very simple expressions are a single data value and with no operations, for example, a single number. More complex expressions involve at least one operation and probably more data values as well, for example, adding two numbers or calculating the area, as shown in the following code example:

import math 
 
def example_function(name: str, radius: float) -> str: 
  area = math.pi * radius ** 2 
  return "The area of {} is {}" .format(name, area)  
 
print(example_function('Bob', 5)) 

All expressions produce a resulting data value of some sort; for example, adding two numbers produces the sum as another number, while concatenating two text strings produces the concatenation as another text string. Using a name variable to look up the stored value is an expression, so is running a function.

Anywhere we need a value, we can use any expression that produces the needed value. It doesn't matter whether the expression is a simple number, such as 55, a variable name, a complex combination of values and operators, a function call, or any other expression. At least, it doesn't matter as far as the final result is concerned. Some expressions take less time to execute than others, so speed can be a factor.