###### 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
```python=
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
```python=
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
```python=
def showMsg(funName):
print('run function: ', funName)
showMsg('add')
showMsg('sub')
```
## 範例四: 有參數、有回傳值
```python=
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
```python=
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)
```python=
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
```python=
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
```
```python=
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
```python=
def add(x, y=10):
return x+y
print(add(5, 12))
print(add(5))
```
## 任意參數數量
```python=
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
```python=
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)
```
```python=
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**
```python=
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
```python=
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
```python=
def sum(num1, num2):
return num1+num2
print(sum(10, 5))
```
```python=
sum = lambda num1, num2: num1 + num2
print(sum(10, 5))
```
## 匿名函數範例
```python=
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
```python=
import smtplib
sender = 'wootu.test@gmail.com' # 你的gmail帳號
sender_password = '' # 你的gmail密碼
receivers = ['amos.tsai@gmail.com'] # 要寄給哪些人
message = """From: From Person <from@fromdomain.com>
To: To Person <to@todomain.com>
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
[關於python*和**的問題](https://github.com/dokelung/Python-QA/blob/master/questions/star/關於python*和**的問題.md)
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