File I/O

File I/O (Input/Output) allows Python programs to read from and write to files.

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Open a File

Use the open() function.

```python id="a1b2c3" file = open("example.txt", "r") content = file.read() file.close()

print(content)

### File Modes

| Mode | Description       |
| ---- | ----------------- |
| `r`  | Read (default)    |
| `w`  | Write (overwrite) |
| `a`  | Append            |
| `x`  | Create new file   |

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## Read a File

### Read Entire File

```python id="d4e5f6"
with open("example.txt", "r") as file:
    content = file.read()
    print(content)

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Read Line by Line

```python id="g7h8i9" with open("example.txt", "r") as file: for line in file: print(line.strip())

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## Write to a File

⚠️ `w` mode will overwrite existing content.

```python id="j1k2l3"
with open("output.txt", "w") as file:
    file.write("Hello Python\n")
    file.write("File I/O example\n")

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Append to a File

```python id="m4n5o6" with open("output.txt", "a") as file: file.write("This is appended text\n")

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## Check File Existence

```python id="p7q8r9"
import os

if os.path.exists("output.txt"):
    print("File exists")
else:
    print("File not found")

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Read File into a List

```python id="s1t2u3" with open("example.txt", "r") as file: lines = file.readlines()

print(lines)

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## Common Pattern: with Statement

Using `with` automatically closes the file.

```python id="v4w5x6"
with open("example.txt", "r") as file:
    content = file.read()

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Summary

• Use open() to work with files
• Use r, w, a modes for reading/writing
• Prefer with statement for safe file handling
• Use read(), readlines(), or iteration to read files
• Always close files if not using with

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