8.1. Function Definition¶

8.1.1. Rationale¶

Reuse code

Improves code readability

Clean-up code

Allows for easier refactoring

8.1.2. Syntax¶

def <name>():
    <do something>

8.1.3. Definition¶

def say_hello():
    print('My name... José Jiménez')

say_hello()     # My name... José Jiménez
say_hello()     # My name... José Jiménez
say_hello()     # My name... José Jiménez

8.1.4. Convention¶

Do not use camelCase names

CamelCase is reserved for class names

Use snake_case names # Python - snake ;)

Add underscore (_) at the end of name when name collide

System functions names starts and ends with 'dunder' - double underscore: __

Listing 8.1. Do not use camelCase, CamelCase is reserved for class names. Use snake_case¶

def sayHello():
    print('This is camelCase() name')
    print('It is c/c++/Java/JavaScript convention')

def say_hello():
    print('This is snake_case() name')
    print('It is Pythonic way')

Listing 8.2. Use better names, rather than comments¶

def cal_var(data, m):
    # Calculate variance
    return sum((Xi-m) ** 2 for Xi in data) / len(data)

def calculate_variance(data, m):
    return sum((Xi-m) ** 2 for Xi in data) / len(data)

Listing 8.3. Add underscore (_) at the end of name when name collide. Although prefer naming it differently.¶

def print_(text):
    # Add underscore (``_``) at the end of name when name collide.
    print(f'<strong>{text}</strong>')

def print_html(text):
    # Although prefer naming it differently.
    print(f'<strong>{text}</strong>')

Listing 8.4. System functions names starts and ends with 'dunder' - double underscore: __¶

def __import__(module_name):
    ...

8.1.5. Docstring¶

Docstring is a first multiline comment in: File/Module, Class, Method/Function

Used for generating help() documentation

It is accessible in __doc__ property of an object

Used for doctest

PEP 257 Docstring convention - For multiline always use three double quote (""") characters

More information in Function Doctest

Listing 8.5. Docstring used for documentation¶

def say_hello():
    """This is the say_hello function"""
    print('Hello')


help(say_hello)
# Help on function say_hello in module __main__:
#
# say_hello()
#     This is the say_hello function

print(say_hello.__doc__)
# This is the say_hello function

Listing 8.6. Docstring used for documentation¶

def say_hello():
    """
    This is the say_hello function
    And the description is longer then one line
    """
    print('Hello')


help(say_hello)
# Help on function say_hello in module __main__:
#
# say_hello()
#     This is the say_hello function
#     And the description is longer then one line

print(say_hello.__doc__)
#    This is the say_hello function
#    And the description is longer then one line

8.1.6. Assignments¶

8.1.6.1. Function Definition Print¶

Complexity level: easy
Lines of code to write: 5 lines
Estimated time of completion: 3 min
Solution: solution/function_definition_print.py

English

Define function call without parameters
Print Beetlejuice on the screen
Call function three times

Polish

Zdefiniuj funkcję call bez parametrów
Wypisz Beetlejuice na ekranie
Wywołaj funkcję trzy razy