dowhen

https://dowhen.readthedocs.io
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dowhen is an instrumentation tool for Python that allows you execute certain code at specific...
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### Install dowhen

Source: https://dowhen.readthedocs.io

Install the dowhen package using pip.

```bash
pip install dowhen

```

--------------------------------

### Basic dowhen Usage: do and when

Source: https://dowhen.readthedocs.io

Execute a simple assignment callback before a function's return statement. The handler can be removed to revert to default behavior.

```python
from dowhen import bp, do, goto, when

def f(x):
    x += 100
    # Let's change the value of x before return
    return x

# do("x = 1") is the callback
# when(f, "return x") is the trigger
# This is equivalent to:
# handler = when(f, "return x").do("x = 1")
handler = do("x = 1").when(f, "return x")
# x = 1 is executed before "return x"
assert f(0) == 1

# You can remove the handler
handler.remove()
assert f(0) == 100

```

--------------------------------

### Chaining Callbacks with dowhen

Source: https://dowhen.readthedocs.io

Chain multiple callbacks like goto() and do() to execute in sequence at a trigger. Handlers do not need to be stored if not explicitly managed.

```python
# You can chain callbacks and they'll run in order
# You don't need to store the handler if you don't use it
when(f, "x += 100").goto("return x").do("x = 42")
assert f(0) == 42

```

--------------------------------

### Using bp() for Debugging

Source: https://dowhen.readthedocs.io

Use the bp() callback to enter pdb at a specific trigger point. Handlers can be temporarily disabled.

```python
# bp() is another callback that brings up pdb
handler = bp().when(f, "return x")
# This will enter pdb
f(0)
# You can temporarily disable the handler
# handler.enable() will enable it again
handler.disable()

```

--------------------------------

### Using goto() to Skip Code

Source: https://dowhen.readthedocs.io

Employ the goto() callback within a context manager to skip specific lines of code. The handler is automatically removed after the context.

```python
# goto() is a callback too
# This will skip the line of `x += 100`
# The handler will be removed after the context
with goto("return x").when(f, "x += 100"):
    assert f(0) == 0

```
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