Add support for pandas eval #137
Description
Hello, I'm running into an issue with using pint_pandas with pandas' eval function:
import pandas as pd
import pint_pandas
df = pd.DataFrame({'a': pd.Series([1., 2., 3.], dtype='pint[meter]'), 'b': pd.Series([4., 5., 6.], dtype='pint[second]')})
# this works as expected
print(df['a'] / df['b'])
"""
0 0.25
1 0.4
2 0.5
dtype: pint[meter / second]
"""
# this is not working
print(df.eval('a / b'))
"""
TypeError: Cannot interpret 'pint[meter]' as a data type
"""The problem arises when pandas tries to check if the columns are numeric by calling this function. This is in turn passed to np.dtype(dtype), which results in the below type error.
It's important for my application to use pandas eval, and the above is just a toy example.
Full stack trace:
Traceback (most recent call last):
File "scratch_8.py", line 8, in <module>
print(df.eval('a / b'))
File "pandas/core/frame.py", line 4240, in eval
return _eval(expr, inplace=inplace, **kwargs)
File "pandas/core/computation/eval.py", line 350, in eval
parsed_expr = Expr(expr, engine=engine, parser=parser, env=env)
File "pandas/core/computation/expr.py", line 811, in __init__
self.terms = self.parse()
File "pandas/core/computation/expr.py", line 830, in parse
return self._visitor.visit(self.expr)
File "pandas/core/computation/expr.py", line 415, in visit
return visitor(node, **kwargs)
File "pandas/core/computation/expr.py", line 421, in visit_Module
return self.visit(expr, **kwargs)
File "pandas/core/computation/expr.py", line 415, in visit
return visitor(node, **kwargs)
File "pandas/core/computation/expr.py", line 424, in visit_Expr
return self.visit(node.value, **kwargs)
File "pandas/core/computation/expr.py", line 415, in visit
return visitor(node, **kwargs)
File "pandas/core/computation/expr.py", line 538, in visit_BinOp
return self._maybe_evaluate_binop(op, op_class, left, right)
File "pandas/core/computation/expr.py", line 505, in _maybe_evaluate_binop
res = op(lhs, rhs)
File "pandas/core/computation/expr.py", line 541, in <lambda>
return lambda lhs, rhs: Div(lhs, rhs)
File "pandas/core/computation/ops.py", line 536, in __init__
if not isnumeric(lhs.return_type) or not isnumeric(rhs.return_type):
File "pandas/core/computation/ops.py", line 520, in isnumeric
return issubclass(np.dtype(dtype).type, np.number)
TypeError: Cannot interpret 'pint[meter]' as a data type