Default and keyword arguments

Intermediate Python for Developers

Jasmin Ludolf

Senior Data Science Content Developer

Average

# Create a custom function
def average(values):
    # Calculate the average
    average_value = sum(values) / len(values)

    # Round the results
    rounded_average = round(average_value, 2)

    # Return rounded_average as an output
    return rounded_average

values = Argument

Arguments

Values provided to a function or method
- Positional
- Keyword

Positional arguments

Provide arguments in order, separated by commas

# Round pi to 2 digits
print(round(3.1415926535, 2))

3.14

Keyword arguments

Provide arguments by assigning values to keywords
Useful for interpretation and tracking arguments

# Round pi to 2 digits 
print(round(number=3.1415926535

Keyword arguments

Provide arguments by assigning values to keywords
Useful for interpretation and tracking arguments

# Round pi to 2 digits 
print(round(number=3.1415926535, ndigits=2))

3.14

Identifying keyword arguments

# Get more information about the help function
print(help(round))

Help on built-in function round in module builtins:

round(number, ndigits=None)
    Round a number to a given precision in decimal digits.

    The return value is an integer if ndigits is omitted or None.  Otherwise,
    the return value has the same type as the number.  ndigits may be negative.

Keyword arguments

Help on built-in function round in module builtins:

round(number, ndigits=None)
  Round a number to a given precision in decimal digits.

  The return value is an integer if ndigits is omitted or None. Otherwise 
  the return value has the same type as the number. ndigits may be negative.

First argument: number
Second argument: ndigits

Default arguments

Help on built-in function round in module builtins:

round(number, ndigits=None)
    Round a number to a given precision in decimal digits.

    The return value is an integer if ndigits is omitted or None.  Otherwise,
    the return value has the same type as the number.  ndigits may be negative.

None = no value / empty
Default argument: way of setting a default value for an argument
We overwrite None to 2
Commonly used value - set it using a default argument

Adding an argument

# Create a custom function
def average(values):
    average_value = sum(values) / len(values)
    rounded_average = round(average_value, 2)
    return rounded_average

Adding an argument

# Create a custom function
def average(values, rounded=False):

Adding an argument

# Create a custom function
def average(values, rounded=False):

    # Round average to two decimal places if rounded is True
    if rounded == True:

        average_value = sum(values) / len(values)
        rounded_average = round(average_value, 2)
        return rounded_average

Adding an argument

# Create a custom function
def average(values, rounded=False):

    # Round average to two decimal places if rounded is True
    if rounded == True:
        average_value = sum(values) / len(values)
        rounded_average = round(average_value, 2)
        return rounded_average

    # Otherwise, don't round
    else:
        average_value = sum(values) / len(values)
        return average_value

Using the modified average() function

# List of preparation times (minutes)
preparation_times = [19.23, 15.67, 48.57, 23.45, 12.06, 34.56, 45.67]

Using the modified average() function

# Get the average without rounding
print(average(preparation_times, False))

28.4585714

# Get the average without rounding
print(average(preparation_times))

28.4585714

Using the modified average() function

# Get the rounded average
print(average(values=preparation_times, rounded=True))

28.46

Let's practice!

Intermediate Python for Developers