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Python Crash Course 8 - Function

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Python Crash Course, 2nd Edition
Python Crash Course, 2nd Edition
By Guang-Ze Yang 7 min read

I’m YouKoutaku. These codes are from the book python_Crash_Course, 2nd edition. I learned python and took these notes for this book.

8.Function

8.1 Define function

def functionname """function detail"""

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def greet_user():
    """a sample greet"""
    print("Hello!")

greet_user()


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Hello!

8.1.1 sent message to function

local value = parameter globle value = argument

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def greet_user(username):
    """a sample greet"""
    print(f"Hello,{username.title()}!")

greet_user('jesse')

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Hello,Jesse!

8.2 argument

8.2.1 position argument

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def describe_pet(animal_type, pet_name): 
    """pet info"""
    print(f"\nI have a {animal_type}.") 
    print(f"My {animal_type}'s name is {pet_name.title()}.")

describe_pet('cat','harry')
describe_pet('dog','smich')

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I have a cat.
My cat's name is Harry.

I have a dog.
My dog's name is Smich.

8.2.2 keyword argument

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def describe_pet(animal_type, pet_name): 
    """pet info"""
    print(f"\nI have a {animal_type}.") 
    print(f"My {animal_type}'s name is {pet_name.title()}.")

describe_pet(animal_type='cat',pet_name='harry')

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I have a cat.
My cat's name is Harry.

8.2.3 Default value

default value can’t be the frist argument

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def describe_pet(animal_type='dog',pet_name): 
    """pet info"""
    print(f"\nI have a {animal_type}.") 
    print(f"My {animal_type}'s name is {pet_name.title()}.")
describe_pet(pet_name='harry')

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  Input In [10]
    def describe_pet(animal_type='dog',pet_name):
                                       ^
SyntaxError: non-default argument follows default argument

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def describe_pet(pet_name, animal_type='dog'): 
    """pet info"""
    print(f"\nI have a {animal_type}.") 
    print(f"My {animal_type}'s name is {pet_name.title()}.")
describe_pet(pet_name='harry')
describe_pet(animal_type='cat',pet_name='harry')

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I have a dog.
My dog's name is Harry.

I have a cat.
My cat's name is Harry.

8.2.4 complex using

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def describe_pet(pet_name, animal_type='dog'):
    """pet info"""
    print(f"\nI have a {animal_type}.") 
    print(f"My {animal_type}'s name is {pet_name.title()}.")

describe_pet('willie') 
describe_pet(pet_name='willie') 

describe_pet('harry', 'hamster') 
describe_pet(pet_name='harry', animal_type='hamster') 
describe_pet(animal_type='hamster', pet_name='harry')



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I have a dog.
My dog's name is Willie.

I have a dog.
My dog's name is Willie.

I have a hamster.
My hamster's name is Harry.

I have a hamster.
My hamster's name is Harry.

I have a hamster.
My hamster's name is Harry.

8.2.5 avoid argument error

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def describe_pet(pet_name, animal_type='dog'):
    """pet info"""
    print(f"\nI have a {animal_type}.") 
    print(f"My {animal_type}'s name is {pet_name.title()}.")

describe_pet()

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---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

Input In [12], in <cell line: 6>()
      3     print(f"\nI have a {animal_type}.") 
      4     print(f"My {animal_type}'s name is {pet_name.title()}.")
----> 6 describe_pet()


TypeError: describe_pet() missing 1 required positional argument: 'pet_name'

8.3 retrun

8.3.1 sample

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def get_formatted_name(first_name, last_name): 
    """retrun full name"""
    full_name = f"{first_name} {last_name}" 
    return full_name.title() 

musician = get_formatted_name('jimi', 'hendrix') 
print(musician)


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Jimi Hendrix

8.3.2 making optional argument

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def get_formatted_name(first_name, last_name, middle_name=''): 
    """retrun full name"""
    full_name = f"{first_name} {middle_name} {last_name}" 
    return full_name.title() 

musician = get_formatted_name('jimi', 'hendrix') 
print(musician)
musician = get_formatted_name('john', 'hooker','lee') 
print(musician)

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Jimi  Hendrix
John Lee Hooker

8.3.3 return dictionary

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def build_person(first_name, last_name):
    """ruturn a dictionary which include a persional info"""
    person = {'first': first_name, 'last': last_name}
    return person

musician = build_person('jimi', 'hendrix')
print(musician)

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{'first': 'jimi', 'last': 'hendrix'}

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def build_person(first_name, last_name, age=None):
    """ruturn a dictionary which include a persional info"""
    person = {'first': first_name, 'last': last_name}
    if age:
        person['age'] = age
    return person

m1 = build_person('jimi', 'hendrix')
m2 = build_person('you', 'koutaku', '18')
print(m1)
print(m2)

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{'first': 'jimi', 'last': 'hendrix'}
{'first': 'you', 'last': 'koutaku', 'age': '18'}

8.3.4 function with while loop

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def get_formatted_name(first_name, last_name): 
    """return full name""" 
    full_name = f"{first_name} {last_name}" 
    return full_name.title()
# a infinity loop！  
while True:
    print("\nPlease tell me your name:") 
    print("(enter 'q' at any time to quit)") 
    f_name = input("First name: ")
    l_name = input("Last name: ")
    if f_name == 'q' or l_name == 'q':
        break
    formatted_name = get_formatted_name(f_name, l_name) 
    print(f"\nHello, {formatted_name}!")

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Please tell me your name:
(enter 'q' at any time to quit)

Hello, You Koutaku!

Please tell me your name:
(enter 'q' at any time to quit)

8.4 fuction to return list

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def greet_users(names): 
    """greet""" 
    for name in names: 
        msg = f"Hello, {name.title()}!"
        print(msg) 

usernames = ['hannah', 'ty', 'margot'] 
greet_users(usernames)

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Hello, Hannah!
Hello, Ty!
Hello, Margot!

8.4.1 change list in function

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olds = ['phone case', 'robot pendant', 'dodecahedron']
news = []

while olds:
    c = olds.pop()
    print(f"Printing model: {c}")
    news.append(c)

print("\nThe folloing models have been printed :")
for new in news:
    print(new)

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Printing model: dodecahedron
Printing model: robot pendant
Printing model: phone case

The folloing models have been printed :
dodecahedron
robot pendant
phone case

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def print_models(olds, news):
    while olds:
        c = olds.pop()
        print(f"Printing model: {c}")
        news.append(c)

def show_new (news):
    print("\nThe following models have been printed:")
    for new in  news:
        print(new)

olds = ['phone case', 'robot pendant', 'dodecahedron']
news = []
print_models(olds,news)
show_new(news)

print(olds)

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Printing model: dodecahedron
Printing model: robot pendant
Printing model: phone case

The following models have been printed:
dodecahedron
robot pendant
phone case
[]

8.4.2 disable change list in function

create a copy of the list to sent function


```python
def print_models(olds, news):
    while olds:
        c = olds.pop()
        print(f"Printing model: {c}")
        news.append(c)

def show_new (news):
    print("\nThe following models have been printed:")
    for new in  news:
        print(new)

olds = ['phone case', 'robot pendant', 'dodecahedron']
news = []
print_models(olds[:], news)
show_new(news)
print(olds)

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Printing model: dodecahedron
Printing model: robot pendant
Printing model: phone case

The following models have been printed:
dodecahedron
robot pendant
phone case
['phone case', 'robot pendant', 'dodecahedron']

8.5 passing any number of arguments

*arguments'name create a tuple to save all of the arguments

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def pizza(*toppings):
    print(toppings)
pizza('pepperoni')
pizza('pepperoni', 'green pepers', 'extra cheese')

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('pepperoni',)
('pepperoni', 'green pepers', 'extra cheese')

8.5.1 Using both of positon arguments and any number of arguments

the any number of arguments must be at the end.

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def pizza(size, *toppings):
    print(f"\nMaking a {size}-inch pizza with the following toppings:")
    for topping in toppings:
        print(f"-{topping}")
pizza(16,'pepperoni')
pizza(12,'pepperoni', 'green pepers', 'extra cheese')

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Making a 16-inch pizza with the following toppings:
-pepperoni

Making a 12-inch pizza with the following toppings:
-pepperoni
-green pepers
-extra cheese

8.5.2 Using any number of keywords arguments

create a any number of arguments(it's a dictionary) by keywords


```python
def profile (first, last, **user_info):
    user_info['f_name'] = first
    user_info['l_name'] = last
    return user_info

user_profile = profile('albert', 'einstein', location='princeton', field='physics')
print(user_profile)

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{'location': 'princeton', 'field': 'physics', 'f_name': 'albert', 'l_name': 'einstein'}

8.6 modules

8.6.1 import modules

module_name.function_name()

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# pizza.py
def pizza(size, *toppings):
    print(f"\nMaking a {size}-inch pizza with the following toppings:")
    for topping in toppings:
        print(f"-{topping}")

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#m_pizza.py
import pizza

pizza.make_pizza(16,'pepperoni')
pizza.make_pizza(12,'pepperoni', 'green pepers', 'extra cheese')

8.6.2 import function

from module_name import function_name

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from pizza import make_pizza

make_pizza(16,'pepperoni')
make_pizza(12,'pepperoni', 'green pepers', 'extra cheese')

8.6.3 using as to rename function

from module_name import function_name as function_newname

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from pizza import make_pizza as mp

mp(16,'pepperoni')
mp(12,'pepperoni', 'green pepers', 'extra cheese')

8.6.4 using as to rename module

import module_name as module_newname

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import pizza as p

p.make_pizza(16,'pepperoni')
p.make_pizza(12,'pepperoni', 'green pepers', 'extra cheese')

8.6.5 import all of the module

from module_name import *

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from pizza import *

make_pizza(16,'pepperoni')
make_pizza(12,'pepperoni', 'green pepers', 'extra cheese')
Programming Language, Python
Python
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