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BUG: query modifies the frame when you compare with = #8828

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BUG: query modifies the frame when you compare with = #8828

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6794d8d
New eval keyword to disallow assignment
onesandzeroes Nov 14, 2014
afe2d47
Add test
onesandzeroes Nov 16, 2014
79e356d
Revert "New eval keyword to disallow assignment"
onesandzeroes Mar 26, 2015
3fe7951
Add new specialized query parser
onesandzeroes Mar 26, 2015
67a44c5
Use 'pandas_query' parser by default for queries
onesandzeroes Mar 26, 2015
70d8345
Update unit test
onesandzeroes Mar 26, 2015
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15 changes: 14 additions & 1 deletion pandas/computation/expr.py
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Original file line number Diff line number Diff line change
Expand Up @@ -589,6 +589,7 @@ def visitor(x, y):

_python_not_supported = frozenset(['Dict', 'Call', 'BoolOp', 'In', 'NotIn'])
_numexpr_supported_calls = frozenset(_reductions + _mathops)
_query_not_supported = frozenset(['Assign'])


@disallow((_unsupported_nodes | _python_not_supported) -
Expand All @@ -602,6 +603,17 @@ def __init__(self, env, engine, parser,
super(PandasExprVisitor, self).__init__(env, engine, parser, preparser)


@disallow((_unsupported_nodes | _python_not_supported | _query_not_supported) -
(_boolop_nodes | frozenset(['BoolOp', 'Attribute', 'In', 'NotIn',
'Tuple'])))
class PandasQueryExprVisitor(BaseExprVisitor):

def __init__(self, env, engine, parser,
preparser=partial(_preparse, f=compose(_replace_locals,
_replace_booleans))):
super(PandasQueryExprVisitor, self).__init__(env, engine, parser, preparser)


@disallow(_unsupported_nodes | _python_not_supported | frozenset(['Not']))
class PythonExprVisitor(BaseExprVisitor):

Expand Down Expand Up @@ -659,4 +671,5 @@ def names(self):
return frozenset(term.name for term in com.flatten(self.terms))


_parsers = {'python': PythonExprVisitor, 'pandas': PandasExprVisitor}
_parsers = {'python': PythonExprVisitor, 'pandas': PandasExprVisitor,
'pandas_query': PandasQueryExprVisitor}
1 change: 1 addition & 0 deletions pandas/core/frame.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1935,6 +1935,7 @@ def query(self, expr, **kwargs):
>>> df[df.a > df.b] # same result as the previous expression
"""
kwargs['level'] = kwargs.pop('level', 0) + 1
kwargs['parser'] = kwargs.pop('parser', 'pandas_query')
res = self.eval(expr, **kwargs)

try:
Expand Down
12 changes: 11 additions & 1 deletion pandas/tests/test_frame.py
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Original file line number Diff line number Diff line change
Expand Up @@ -15210,7 +15210,7 @@ class TestDataFrameQueryPythonPandas(TestDataFrameQueryNumExprPandas):
def setUpClass(cls):
super(TestDataFrameQueryPythonPandas, cls).setUpClass()
cls.engine = 'python'
cls.parser = 'pandas'
cls.parser = 'pandas_query'
cls.frame = _frame.copy()

def test_query_builtin(self):
Expand All @@ -15225,6 +15225,16 @@ def test_query_builtin(self):
result = df.query('sin > 5', engine=engine, parser=parser)
tm.assert_frame_equal(expected, result)

def test_query_with_assign_statement(self):
df = DataFrame({'a': [1, 2, 3], 'b': ['a', 'b', 'c']})
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can you add the issue number as a comment here

a_before = df['a'].copy()
self.assertRaisesRegexp(
NotImplementedError, "'Assign' nodes are not implemented",
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Not a big deal (and you don't need to fix it here), but in an ideal world this should be something closer to SyntaxError, rather than NotImplementedError. NotImplementedError is really for abstract methods that should be overridden in a subclass or for features that genuinely have not been implemented yet. This is different: if = ever works in query it would be a bug.

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NotImplementedError is what you currently get when you do unsupported operations within a query/eval and hit an unsupported node, e.g.:

import pandas as pd
df = pd.DataFrame({'a': [1, 2, 3], 'b': ['a', 'b', 'c']})
df.eval("{'x': 1}")
NotImplementedError 
/home/me/.local/lib/python2.7/site-packages/pandas/computation/expr.pyc in visit(self, node, **kwargs)
    312         method = 'visit_' + node.__class__.__name__
    313         visitor = getattr(self, method)
--> 314         return visitor(node, **kwargs)
    315 
    316     def visit_Module(self, node, **kwargs):

/home/me/.local/lib/python2.7/site-packages/pandas/computation/expr.pyc in f(self, *args, **kwargs)
    203     def f(self, *args, **kwargs):
    204         raise NotImplementedError("{0!r} nodes are not "
--> 205                                   "implemented".format(node_name))
    206     return f
    207 
NotImplementedError: 'Dict' nodes are not implemented

So at the moment it's just working like any other invalid query/eval. For this specific case I'll probably try to catch the exception within DataFrame.query() and spit out a more meaningful
message. Not sure where you'd have to intercept the exception if you wanted to raise more
meaningful error messages from eval more generally.

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the NotImplementedError is fine. I agree ideally should be SyntaxError but that's a separate change (welcome to make an issue if so desired)

df.query, 'a=1', engine=self.engine, parser=self.parser
)
a_after = df['a'].copy()
assert_series_equal(a_before, a_after)


class TestDataFrameQueryPythonPython(TestDataFrameQueryNumExprPython):

Expand Down