# Python Signal Module

The `signal` module provides mechanisms to use signal handlers in Python. Signals are software interrupts delivered to a process by the operating system.

## Importing the Module

```python
import signal
import sys
import time
```

## Handling Signals

To handle a signal, you define a handler function. This function takes two arguments: the signal number and the current stack frame.

```python
def signal_handler(sig, frame):
    print('You pressed Ctrl+C!')
    sys.exit(0)
```

## Registering a Handler

Use `signal.signal()` to register a handler for a specific signal.

```python
# Register the handler for SIGINT (Ctrl+C)
signal.signal(signal.SIGINT, signal_handler)

print('Press Ctrl+C')
while True:
    time.sleep(1)
```

## Common Signals

*   `signal.SIGINT`: Interrupt from keyboard (Ctrl+C).
*   `signal.SIGTERM`: Termination signal.
*   `signal.SIGKILL`: Kill signal (cannot be caught or ignored).
*   `signal.SIGALRM`: Timer signal (Unix only).

## Alarms (Unix Only)

On Unix-based systems, you can use `signal.alarm()` to schedule a `SIGALRM` signal.

```python
def handler(signum, frame):
    raise Exception("Timeout")

# Register the signal function handler
signal.signal(signal.SIGALRM, handler)

# Define a 2-second alarm
signal.alarm(2)

try:
    time.sleep(10)
except Exception as exc: 
    print(exc)
```

## Ignoring Signals

You can ignore a signal by setting the handler to `signal.SIG_IGN`.

```python
signal.signal(signal.SIGINT, signal.SIG_IGN)
```

[[programming/python/python]]