# l.Python - 檔案讀寫
###### tags: `Python`
## 1.開啟檔案
* <font color="#0080FF">**絕對路徑、讀取**</font>
```python=+
import os
file_name = os.path.join('C:\\','Users','tonyc','pythonwork','document','test.txt')
with open(file_name,'r') as file:
line = file.readline() #讀取一整行(包含「\n」)
print(line)
```
> ```Hello World!!!!!!!!!```</br>
> ``` ```
##
* <font color="#0080FF">**寫入模式**</font>
```python=+
file = open('C:\\Users\\tonyc\\pythonwork\\document\\hello.txt','w')
file.write('Hello World!')
file.close()
```
##
<font color="#0080FF">**hello.txt**</font>
```python=+
Hello World!
```
##
* <font color="#0080FF">**附加模式**</font>
```python=+
file = open('C:\\Users\\tonyc\\pythonwork\\document\\hello.txt','a')
file.write('\nHello Python!')
file.close()
```
<font color="#0080FF">**hello.txt**</font>
```python=+
Hello World!
Hello Python!
```
##
* <font color="#0080FF">**編碼格式 encoding**</font>
> <font color="#EA0000">**open()函式會以作業系統預設編碼來開啟檔案，而繁體中文 Windows 預設編碼格式為「cp950」。通常都會改設為「utf-8」和「utf-8-sig」( 大小寫均可，「-」可換成「_」)</br></br>utf-8-sig : 檔案最前面加上BOM( Byte-order mark )，以便辨識此檔案的編碼方式，不過若軟體、程式不支援則會變成亂碼**</font>
## 2.讀取文字檔和二進位檔案
* <font color="#0080FF">**readline() 讀取一行**</font>
```python=+
file = open('C:\\Users\\tonyc\\pythonwork\\document\\test.txt','r')
count = 0
while file.readline() != '':
#計算檔案行數
count += 1
print(count)
file.close()
```
> ```3```
##
* <font color="#0080FF">**readlines() 讀取所有行**</font>
```python=+
file = open('C:\\Users\\tonyc\\pythonwork\\document\\test.txt','r')
print(len(file.readlines()))
file.close() #readline 和 readlines 皆可用參數指定每次讀取資料量
```
> ```3```
##
* <font color="#0080FF">**用 For 迴圈逐行讀取檔案 ( 推薦，不會耗盡記憶體 )**</font>
```python=+
file = open('C:\\Users\\tonyc\\pythonwork\\document\\test.txt','r')
for line in file: #會包含換行符號
print(line)
file.close()
```
> ```Hello World!!!!!!!!!```</br>
> ``` ```</br>
> ```!!!!!!!!!Hello World```</br>
> ``` ```</br>
> ```!!!!Hello World!!!!!```</br>
> ``` ```
##
* <font color="#0080FF">**處理換行符號**</font>
```python=+
#強制只將「\n」視為換行符號 (關閉自動轉換功能)
input_file = open('myfile',newline = '\n')
```
## 3.寫入檔案
* <font color="#0080FF">**write() 寫入字串資料**</font>
```python=+
myfile.write('Hello\nWorld')
```
##
* <font color="#0080FF">**writelines() 寫入陣列資料**</font>
```python=+
#檔案內容複製( 驗證 writelines() 是 readlines() 的反函式 )
path = os.path.join(os.pardir,'document','myfile.txt')
input_file = open(path,'r')
lines = input_file.readlines() #readlines為陣列格式
input_file.close()
print('>> 寫入output_file...\n內容 :',lines)
path = os.path.join(os.pardir,'document','myfile2.txt')
output_file = open(path,'w')
output_file.writelines(lines) # writelines不會在陣列中加入換行,必須手動
print('>> 寫入成功...')
output_file.close()
```
> ```>> 寫入output_file...```</br>
> ```內容 : ['Hello Python!!!!!!!!!\n', '!!!!!!!!!Hello Python\n', '!!!!Hello Python!!!!!']```</br>
> ```>> 寫入成功...```
##
* <font color="#0080FF">**myfile.txt、myfile2.txt**</font>
```python=+
Hello Python!!!!!!!!!
!!!!!!!!!Hello Python
!!!!Hello Python!!!!!
```
## 4.讀取與寫入 - pathlib
* <font color="#0080FF">**建立 Path 物件處理文字檔與二進位檔**</font>
```python=+
from pathlib import Path
p_text = Path('my_text_file')
p_text.write_text('Text file contents') #傳回寫入的字串長度
p_text.read_text() #傳回字串內容
p_binary = Path('my_binary_file')
p_binary.write_bytes(b'Binary file contents') #傳回寫入的位元組長度
p_binary.read_bytes() #傳回位元組內容
```
> ```18```</br>
> ```Text file contents```</br>
> ```20```</br>
> ```b'Binary file contents'```
## 5.標準輸入 / 輸出與重新導向
* <font color="#0080FF">**將標準輸出「重新導向」至檔案及回復其原始值**</font>
```python=+
import sys,os
savedout = sys.stdout #(注意!)IDLE中sys.stdout初值為PseudoOutputFile物件，與sys.__stdout__並不相同
path = os.path.join(os.pardir,'document','outfile2.txt')
f = open(path,'w')
sys.stdout = f #將標準輸出「重新導向」到檔案
sys.stdout.writelines(['A first line.\n','A second line.\n'])
print('A line from the print function.')
3 + 4 #(注意!)在IDLE情況下，似乎無法寫入檔案
sys.stdout = savedout #將標準輸出回復為原始值
f.close()
print('Hello')
3 + 4
```
> ```Hello```</br>
> ```7```
##
* <font color="#0080FF">**不改變標準輸出，並重新導向至檔案**</font>
```python=+
import os
path = os.path.join(os.pardir,'document','outfile3.txt')
f = open(path,'w')
print('A first line.','\nA second line.',file = f) #這兩個字串會輸出到檔案物件f
pritn(3 + 4)
f.close()
3 + 4
```
> ```7```</br>
> ```7```
## 6.讀取結構化二進位資料
* <font color="#0080FF">**struct 模組**</font>
**(SKIP)**
## 7.將物件序列化後保存到檔案
* <font color="#0080FF">**pickle 模組 保存重要的變數**</font>
```python=+
import pickle
path = os.path.join(os.pardir,'document','pickle.txt')
file = open(path,'wb')
a = 'Hello'
b = list('Hello')
c = {'H':'ello'}
#pickle可儲存各種型態的資料
pickle.dump(a,file)
pickle.dump(b,file)
pickle.dump(c,file)
file.close()
```
##
<font color="#0080FF">**pickle.txt**</font>
```python=+
X Helloq .]q (X HqX eqX lqhX oqe.}q X HqX elloqs.
```
##
* <font color="#0080FF">**pickle 模組 讀取儲存資料**</font>
```python=+
import pickle
path = os.path.join(os.pardir,'document','pickle.txt')
file = open(path,'rb')
a = pickle.load(file)
b = pickle.load(file)
c = pickle.load(file)
file.close()
print(a,b,c)
```
> ```Hello ['H', 'e', 'l', 'l', 'o'] {'H': 'ello'}```
## 8.利用字典的鍵取得大量資料
* <font color="#0080FF">**shelve 物件**</font>
> <font color="#EA0000">**可將其視為一個字典，該字典的資料是儲存在磁碟機上而不是記憶體，因此無須受到記憶體大小的限制 (優點)**</font>
##
* <font color="#0080FF">**shelve 儲存字典**</font>
```python=+
import shelve
book = shelve.open('address')
book['167'] = ('小明','0912-345678','咪喵路1號')
book['928'] = ('小美','0987-654321','咪喵路2號')
book.close()
```
##
* <font color="#0080FF">**shelve 讀取字典**</font>
```python=+
import shelve
book = shelve.open('address')
book['167']
```
> ```('小明', '0912-345678', '咪喵路1號')```
## 時間戳記
> [name=ZEOxO][time=Tue, Sep 8, 2020 16:15 PM][color=#907bf7]
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