# python_notes

Just notes on various things

## Naming Notes
Classes use CamelCaps
Functions and varibles are lowercase() or lowercase_with_underscores().

Always use self for the first argument to instance methods.
Always use cls for the first argument to class methods

## Magic Methods
Classes have certain magic methods that help make objects behave in pythonlike ways.

* `__repr__` returns a string representation of the object. Should be unambiguous. (i.e. add parameters).
* `__str__` returns a string representation of the object. Should be easily readable but not necessarily
  unambiguous. Careful, can be confused with `__repr__` in some cases. 

## Comments
Block comments are at the same indentation and are complete sentences.
Inline comments shouldn't state the obvious.

Avoid:
```
x = x + 1  # Increment x
```

But this can be useful:
```
x = x + 1  # Compensate for the border
```

## docstrings
Use 'em.
See PEP257 - https://www.python.org/dev/peps/pep-0257

### doctest
In your docstring, put examples that look like the command-line, such as
```
def square(x):
    """
    Returns x times itself.
    >>> square(2)
    4
    """
    return x*x
```
Then `import doctest` and `doctest.testmod()` inside `__main__`, and python will run the
tests to verify correctness.

Run with `python -v` to see the output of the doctest module.

## ArgParse


## Interesting Tidbits
Redirect stdout to a file. The `with` isolates context and prevents certain race conditions, handling errors appropriately.
```
with open('help.txt', 'w') as f:
    with redirect_stdout(f):
        help(pow)
```

### Caching

If you have a function that always returns the same result for a given input, you can cache the result by prefacing with `@lru_cache`. e.g.
```
from functools import lru_cache

@lru_cache(maxsize=32)
def fib(n):
    if n < 2:
        return n
    return fib(n-1) + fib(n-2)
```