# Call a function in Python

Keywords: function, call function, input parameters, arguments

By creating and call multiple small functions in Python, these can be used to create large applications. This makes it much easier to program because you do not have to code the same thing several times.

## How to use a function in Python?

When you want to use a function, it’s called that you call that function. To call a function in Python:

• You enter the function name
• Followed by any input parameters
• When an input parameter is passed to the function, it is denominated as an argument

## Example : Create and Call functions in Python

Let’s start by creating a function that calculates the area of a circle.

• The only input parameter that the function will have is the radius.
• So we send in the radius and will receive the calculated area back.
```import math
"Return area of a circle"

We can test the function by calling it. Examples where the radius of the circle is 4 or 8:

```print("The Area of the circle is ", area_circle(4))
print("The Area of the circle is ", area_circle(8))```

Resulting in

```The Area of the circle is 50.26548245743669
The Area of the circle is 201.06192982974676```

Additionally, in a similar way we create a function that calculates the area of a square.

• Input is the width of the square
• Get back the area of the square
```def area_square(x):
"Returns the area of a square"
return x*x```

Furthermore, we can call the function when, for example, the width is 2, or 5:

```print ("The area of the square is ", area square (2))
print ("The area of the square is ", area_square (5))```

Resulting in

```The area of the square is 4
The area of the square is 25```

We will use the width of the square and the radius of the circle as inparameters

```def largest_area(width, radius):
"Returns if the square or circle has the largest area, given the width of the square and the radius of the circle"

# Calls the function that calculates the area of the square
square = area_square(width)

# Calls the function that calculates the area of the circle

# Determines if the square or circle is largest
if square == circle:
print("The square and circle are the same size!")
elif square > circle:
print("The square has a larger area than the circle")
else:
print("The circle has a larger area than the square")

print("The area of the square is", square, "and the area of the circle is", circle)```

Note, the highlighted rows in the code above is where we call our previous created functions.

Okay, so let’s try our new function. Say that we call the function, for example, when the width of the square is 4 and the radius of the circle is 3:

`largest_area(width=4, radius=3)`

Resulting in:

```The circle has a larger area than the square
The area of the square is 16 and the area of the circle is 28.274333882308138```

Now you can use your finished function as many times as you want, without having to program new code! Additionally, you can add new functions. For example, if you want to compare the perimeter

By creating multiple small functions in Python, these can be used to create large applications.

## Define standard parameters for functions in Python

If desired, you can also define default parameters for a function.

```def dummy_function(text="Programming in Python"):
print("The text that is printed is:", text)```

If no input parameter is specified in this case, the input parameter automatically becomes “Programming in Python”.

You call the function without and with the inparameter

```dummy_function()
dummy_function("New input parameter")```

Resulting in

```The text that is printed is: Programming in Python
The text that is printed is: New input parameter```