定義一個函數
For example,
def greet_user():#定義函數
print("Hello!")
Now, we just need to input greet_user() and Hello! will be shown on the screen.
o 向函數傳遞信息
其實這一點和C語言基本是一致的。這個函數其實就是一個子函數，可以通過括號中的參數向子函數傳遞信息。
例子：
# -*-coding: utf-8 -*-
def greet_user(username):
print("Hello!" + username.title())
name = input("Please input your name.\n")
greet_user(name)
在這裏面，形參就是指子函數def greet_user(username)括號裏面的，實參就是最後一行裏面的name所代表的。
o 關鍵字實參
def describe_pets(animal_type, pet_name):
print("\nI have a " + animal_type + ".")
print("My " + animal_type + "'s name is " + pet_name.title() + ".")
describe_pets(animal_type = 'cat', pet_name = 'hurry')#關鍵字實參
關鍵字實參的順序無關緊要。但是普通的順序必然非常重要。
o 默認值
def describe_pets(pet_name, animal_type = 'dog'):#默認值設置
print("\nI have a " + animal_type + ".")
print("My " + animal_type + "'s name is " + pet_name.title() + ".")
#typ = input("Please input the type of your pet.\n")
#name = input("Please input its name.\n")
#describe_pets(typ,name)
describe_pets(pet_name = 'hurry')#關鍵字實參
設置了默認值之後，默認值項得在形參括號中的最後。設置默認值之後，如果該參數不再修改，那麼這個參數就自動爲默認值，但是如果後面對其進行了傳遞，則使用傳遞的值而不再是默認值。設置了默認值之後，實參可以少一個（本例中，實參只剩1個）
· 返回值
o 返回簡單值。此處返回值與C語言中類似。
o 讓實參變成可選。可以利用指定一個默認值，即爲空值即可。用到就在後面實參裏寫上，用不着就直接用默認的空。
o 返回字典。例如，
def build_person(first_name, last_name):
person = {'first': first_name,'last': last_name}
return person
musician = build_person('jimi', 'hendrix')
print(musician)
· 傳遞列表
o 在函數中修改列表
For example,
def print_models(unprinted_designs, completed_models):
while unprinted_designs:
current_design = unprinted_designs.pop()
print("Printing model: " + current_design)
completed_models.append(current_design)
Finally, unprinted_designs will not have any element. But, what if we want to retain these elements? The answer is as followed:
Use slice. function_name(list_name[:]).
For example, when we call function print_models(unprinted_designs, completed_models),we need to change it to print_models(unprinted_designs[:], completed_models).
· Pass lots of actual parameter
o Using *name as a formal parameter, this is just like a list.. For example,
def make_pizza(*toppings):
print(toppings)
make_pizza('mushrooms', 'green peppers', 'extra cheese')
o Using **name as a formal parameter, this is just like a dict.
· Import functions(★★★★★)
o Import whole function
For example,
import pizza #There is a function file called pizza.py
pizza.make_pizza(16, 'pepperoni') # We need to point out the function from which file
o Import specific function
from module_name import function_name
If we use this, we do not need to point out the function from which file.
· Using as to specifying aliases for functions(用as爲函數指定別名)/using as to specifying aliases for module（用as爲模塊指定別名）/import all functions from module.
o from pizza import make_pizza as mp
o import pizza as p
o from pizza import *