# Python Readline Module

The `readline` module defines a number of functions to facilitate completion and reading/writing of history files from the Python interpreter. This module is based on the GNU Readline library, but it is not available on all platforms (specifically Windows, though `pyreadline` is a common alternative).

## Importing the Module

```python
import readline
```

## Basic Usage

Simply importing `readline` will cause the `input()` function to use readline for line editing and history.

## Auto-Completion

You can register a completer function to assist with tab-completion.

```python
import readline

def completer(text, state):
    options = [i for i in commands if i.startswith(text)]
    if state < len(options):
        return options[state]
    else:
        return None

commands = ['start', 'stop', 'list', 'print']

readline.parse_and_bind("tab: complete")
readline.set_completer(completer)

input('Enter command: ')
```

## History

The module allows you to save and load command history.

### Reading History

```python
import readline
import os

histfile = os.path.join(os.path.expanduser("~"), ".python_history")
try:
    readline.read_history_file(histfile)
    # default history len is -1 (infinite), which may grow unruly
    readline.set_history_length(1000)
except FileNotFoundError:
    pass
```

### Writing History

```python
import atexit
import readline
import os

histfile = os.path.join(os.path.expanduser("~"), ".python_history")
atexit.register(readline.write_history_file, histfile)
```

## Startup File

The `readline` module can execute an initialization file (like `.inputrc`).

```python
readline.read_init_file()
```

[[programming/python/python]]