envopt 0.0.1

Wrap docopt to allow ENV variables as argument defaults

# envopt
Wrapper for [docopt](https://github.com/docopt/docopt) to allow ENV variables to override default arguments.


## Usage

Example docopt pydoc:

```python
__doc__ = \
""" This is an example.

Usage:
python my_example.py [options]

Options:
-a --a-opt OPT # An example long option [default: foo]
-b OPT # An example short option [default: bar]
--cee # An example long switch option
-d # An example short switch option """
```

Parsing this example without any `ENV` variables set would yield:

```python
from envopt import envopt

print envopt(__doc__)

{ '--a-opt' : 'foo',
'-b' : 'bar',
'--cee' : False,
'-d' : False }
```

However, setting `ENV` variables `A_OPT`, `B`, `CEE`, or `D` will override the given defaults:

```python
import os
from envopt import envopt

os.environ['A_OPT'] = 'fizz'
os.environ['B'] = '1'
os.environ['CEE'] = 'buzz'
os.environ['D'] = '1'

print envopt(__doc__)

{ '--a-opt' : 'fizz',
'-b' : 'buzz',
'--cee' : True,
'-d' : True }
```

For switch-style arguments, the existence of the `ENV` variable is enough to set the value to `True`. Unset the variable to return the default value to `False`.

Specifying a `env_prefix` value in the `envopt()` call will prefix `ENV` variables with this prefix right-padded with an underscore:

```python
import os
from envopt import envopt

os.environ['MY_A_OPT'] = 'fizz'
os.environ['MY_B'] = '1'
os.environ['MY_CEE'] = 'buzz'
os.environ['MY_D'] = '1'

print envopt(__doc__, env_prefix='MY')

{ '--a-opt' : 'fizz',
'-b' : 'buzz',
'--cee' : True,
'-d' : True }
```