# 10. 檔案讀寫
## I. 讀檔
通常有兩種方式：\
方法一：
```python
f = open(<檔名>) # 讀檔一般習慣將它存在名稱為f的變數裡
```
不過使用完畢後要記得關閉它
```python
f.close()
```
方法二：\
【此方式使用完畢後會自動關閉檔案，因此較推薦】
```python
with open(<檔名>) as f:
```
【比較看看】
> 假設你現在正在編輯的檔案名稱為`main.py`請你在同個目錄下創造出另一個`.py`(如圖中的`moduleA.py`)檔並嘗試用程式`open`它\
> 
方法一：
```python
f = open("moduleA.py")
print(f.closed) # False (還未關閉)
f.close()
```
方法二：
```python
with open("moduleA.py") as f:
print(f.closed) # False (還未關閉)
print(f.closed) # True (已關閉)
```
### A.開檔模式
開啟檔案時需指名開檔模式，根據開啟的模式，只能使用限定的功能\
寫法：【`open(<檔名>, <模式>)`】
| 模式 | 功能 | 若存在此檔名 | 寫入方式 | 若不存在此檔名 |
| -- | ----- | ------ | ------------------------------ | ------- |
| r | 讀取 | 讀取 | | Error |
| r+ | 寫入+讀取 | 讀取 | 從第一列開始覆蓋
(並沒有整個檔案覆蓋)
| Error |
| w | 寫入 | 整個檔案覆蓋 | 整個檔案覆蓋 | 開新檔案 |
| w+ | 寫入+讀取 | 整個檔案覆蓋 | 整個檔案覆蓋 | 開新檔案 |
| a | 寫入 | 讀取 | 接續 | 開新檔案 |
| a+ | 寫入+讀取 | 讀取 | 接續 | 開新檔案 |
### B.開檔後讀取檔案內容
```python
with open("moduleA.py", "r") as f:
s = f.read()
print(s)
```
## II.寫檔
### A. 開檔後寫入檔案內容
【試試看看】
> 下列三種方法的結果有何不同?
```python
# 請先自行新增file_r.txt空檔
for k in range(3):
with open('file_r.txt', 'r+') as f:
f.write(f'this is line {k}\n')
```
```python
# 請先自行新增file_w.txt空檔
for k in range(3):
with open('file_w.txt', 'w+') as f:
f.write(f'this is line {k}\n')
```
```python
# 請先自行新增file_a.txt空檔
for k in range(3):
with open('file_a.txt', 'a+') as f:
f.write(f'this is line {k}\n')
```
### B. 開檔後先寫入再讀取檔案內容
【試試看看】
> 下列三種個`.txt`檔都請先事先設為：
```python
line: 70
line: 80
line: 90
line: 20
line: 10
line: 00
```
再開始測試下列三種讀寫檔案方式：
```python
with open('file_r.txt', 'r+') as f:
for k in range(3):
f.write(f'line: {k} \n')
f.seek(0) # 回到檔案第一列第一行
print(f.read())
```
```python
with open('file_w.txt', 'w+') as f:
for k in range(3):
f.write(f'line: {k} \n')
f.seek(0) # 回到檔案第一列第一行
print(f.read())
```
```python
with open('file_a.txt', 'a+') as f:
for k in range(3):
f.write(f'line: {k} \n')
f.seek(0) # 回到檔案第一列第一行
print(f.read())
```
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