Unable to decorate a class method using Pint units
<p>Here's a very simple example in an effort to decorate a class method using Pint,</p>

<pre><code>from pint import UnitRegistry

ureg = UnitRegistry()
Q_ = ureg.Quantity

class Simple:
    def __init__(self):
    pass

@ureg.wraps('m/s', (None, 'm/s'), True)
def calculate(self, a, b):
    return a*b

if __name__ == "__main__":
    c = Simple().calculate(1, Q_(10, 'm/s'))
    print c
</code></pre>

<p>This code results in the below ValueError.</p>

<pre><code>Traceback (most recent call last):
   c = Simple().calculate(1, Q_(10, 'm/s'))
   File "build/bdist.macosx-10.11-intel/egg/pint/registry_helpers.py",   line 167, in wrapper
   File "build/bdist.macosx-10.11-intel/egg/pint/registry_helpers.py", line 118, in _converter
   ValueError: A wrapped function using strict=True requires quantity for all arguments with not None units. (error found for m / s, 1)
</code></pre>

<p>It seems to me that the issue here may be with class instances being passed to the pint decorator. Would anyone have a solution for fixing this?</p>

<p>Thanks for the answer. Keeping the strict mode, your first answer produces an output, i.e. make the first argument a pint Quantity too. However, the units of the output include a multiplication of the output unit specified in the wrapper and the units of the first argument too, which is incorrect. </p>

<p>The solution is just to add another 'None' to the wrapper to account for the class instance, i.e.</p>

<pre><code>@ureg.wraps('m/s', (None, None, 'm/s'), True)
def calculate(self, a, b):
    return a*b
</code></pre>

python pint