tags: python

函數

特性

• 將重複撰寫的程式碼以函數的架構重新整理
• 給予這段程式碼一個有意義的名稱(函數名稱)
• 當要使用該功能時呼叫該函數即可
• 可以讓程式更加簡潔、意義化、可重複使用、降低錯誤率、方便維護

函數來源

• 語言內建: print(), input(), type() …
• 第三方模組/函數庫: wxPython, matplotlib …
• 自行開發

注意

• 函數必須先定義才能呼叫

---

範例一: 無參數、無回傳值

def showMsg(): # 定義有個函數叫showMsg
    print("hello")
    
showMsg() # 呼叫showMsg函數

範例二: 無參數、有回傳值

count = 0

def counts():
    global count # 使用全域變數
    count = count + 1
    return count

print(counts())
print(counts())

範例四: 有參數、無回傳值

def showMsg(funName):
    print('run function: ', funName)

showMsg('add')
showMsg('sub')

範例四: 有參數、有回傳值

def add(num1, num2):
    return num1 + num2

result = add(3, 6)
print("result =", result) # result = 9

result = add(32, 26)
print("result =", result) # result = 58

---

參數傳遞方式

傳值呼叫

預設傳值: 數值、字串、tuple

def swap(x, y):
    print('x = {0}, y = {1}'.format(x, y))
    x, y = y, x
    print('x = {0}, y = {1}'.format(x, y))
    
a, b = 1, 2
print(a, b)
swap(a, b)
print(a, b) # swap並沒有改變a, b的值

傳址呼叫

預設傳址: list(串列), set(集合), dict(字典)

def swap(x):
    print('x[0] = {0}, x[1] = {1}'.format(x[0], x[1]))
    x[0], x[1] = x[1], x[0]
    print('x[0] = {0}, x[1] = {1}'.format(x[0], x[1]))
    
x = [1, 5]
print(x[0], x[1])
swap(x)
print(x[0], x[1]) # swap改變x的內容順序

關鍵字參數

沒有指定照傳入順序，有指定照指定設定
指定參數必須放在無指定參數的後面

def showMsg(person1, person2):
    print('{0} 喜歡 {1}'.format(person1, person2))

showMsg('小明', '小華')
showMsg(person2='小明', person1='小華')
showMsg('小華', person2='小明') # 正確
showMsg('小華', person1='小明') # 錯誤，person1已經被指定微小華
showMsg(person2='小明', '小華') # 錯誤，無指定參數必須放在指定參數之前

str1 = '{0} love {1}'
str2 = '{0} like {1}'

print(str1)
print(str2)

str3 = str1.format('amos', 'carol')
str4 = str2.format('amos', 'carol')

print(str3)
print(str4)

str5 = '{name} is {year} old {name}'
str6 = str5.format(name='amos', year=18, gen='man')

print(str5)
print(str6)

參數預設值

當沒有指定參數值時使用預設值

def add(x, y=10):
    return x+y

print(add(5, 12))
print(add(5))

任意參數數量

def add(*num):  # 將多個打包成一個
    total = 0
    for i in num:
        total += i
    
    return total

print(add(3))
print(add(3, 5))
print(add(3, 5, 112))


# -----------------------------
def add(num1, num2, num3, num4, num5):
    return num1 + num2 + num3 + num4 + num5


data = (3, 5, 9, 10, 15)

print( add(*data) )  # 將一個拆成多個
# add(data[0], data[1], data[2], data[3], data[4])

任意字典參數數量

def intro(id, name, years, location):
    msg = '''
        編號: {0}
        姓名: {1}
        年資: {2}
        廠區: {3}'''.format(id, name, years, location)
    
    print(msg)

intro(1, 'amos', 10, 'taipei')

one = [1, 'amos', 10, 'taipei']
# intro(one[0], one[1], one[2], one[3])
intro(*one)

two = {'id': 1, 'name': 'amos', 'years': 10, 'location': 'taipei'}
# intro(two['id'], two['name'], two['years'], two['location'])
intro(**two)

def intro(**info):
    msg = '''
        編號: {0}
        姓名: {1}
        年資: {2}
        廠區: {3}'''.format(info['id'], info['name'], info['year'], info['location'])
    
    print(msg)


intro(id=1, name='amos', year=10, location='taipei')

三種參數種類使用順序

必須遵守以下順序:
參數, 任意數量, 任意字典參數

def info(name, *args, **kwargs):
    print('name: ', name)
    
    for i in args:
        print(i)
        
    for key, value in kwargs.items():
        print('{0} = {1}'.format(key, value))

info('amos', '111', 'taipei', language='python', DB='mySQL')

# name:  amos
# 111
# taipei
# language = python
# DB = mySQL

---

區域變數, 全域變數

num1 = 5
num2 = 5

def add():
    num1 = 10
    print('在函數中的num1: ', num1)
    
    global num2
    num2 += 30
    print('在函數中的num2: ', num2)

print('在函數外的: ', num1)
print('在函數外的: ', num2)
print('===========================')
add()
print('在函數外的: ', num1)
print('在函數外的: ', num2)

---

匿名函數(lambda)

• 當有些函數本身非常簡單，只有一個運算式
• 該函數使用頻率很低
• 讓程式碼更簡潔(但執行效能不變)
• 函數內容只能放運算式，不能放指派運算式(例如: x=5)
• 通常與map、reduce、filter函數一起使用

def sum(num1, num2):
    return num1+num2

print(sum(10, 5))

sum = lambda num1, num2: num1 + num2

print(sum(10, 5))

匿名函數範例

pern = [
    ('Mary', 1988, 'taipei'),
    ('Davie', 1992, 'kaohsiung'),
    ('Andy', 1999, 'taichung')
]

st = lambda item: item[0]

i = pern[0]  # ('Mary', 1988, 'taipei')
j = st(i)  # 'Mary'
print(j)


pern.sort(key = st)

for name in pern:
    print('{0}, {1}, {2}'.format(*name))

用python來寄信

import smtplib

sender = '[e-mail]' # 你的gmail帳號
sender_password = '' # 你的gmail密碼
receivers = ['[e-mail]'] # 要寄給哪些人

message = """From: From Person <[e-mail]>
To: To Person <[e-mail]>
Subject: SMTP e-mail test

This is a test e-mail message.
""" # 信件內容

smtpObj = smtplib.SMTP('smtp.gmail.com', 587)
smtpObj.ehlo()
smtpObj.starttls()
smtpObj.ehlo()
smtpObj.login(sender, sender_password)
smtpObj.sendmail(sender, receivers, message)
smtpObj.quit()

參考資料

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