CLN: core.computation, mostly typing

pandas/core/computation/align.py

@@ -33,7 +33,7 @@ def _zip_axes_from_type(typ, new_axes):
     return axes
 
 
-def _any_pandas_objects(terms):
+def _any_pandas_objects(terms) -> bool:
     """Check a sequence of terms for instances of PandasObject."""
     return any(isinstance(term.value, PandasObject) for term in terms)
 
@@ -144,7 +144,8 @@ def _reconstruct_object(typ, obj, axes, dtype):
     obj : object
         The value to use in the type constructor
     axes : dict
-        The axes to use to construct the resulting pandas object
+        The axes to use to construct the resulting pandas object.
+    dtype : numpy dtype
 
     Returns
     -------

pandas/core/computation/engines.py

@@ -22,7 +22,7 @@ def _check_ne_builtin_clash(expr):
 
     Parameters
     ----------
-    terms : Term
+    expr : Term
         Terms can contain
     """
     names = expr.names
@@ -46,8 +46,9 @@ def __init__(self, expr):
         self.aligned_axes = None
         self.result_type = None
 
-    def convert(self):
-        """Convert an expression for evaluation.
+    def convert(self) -> str:
+        """
+        Convert an expression for evaluation.
 
         Defaults to return the expression as a string.
         """
@@ -75,10 +76,9 @@ def evaluate(self):
         )
 
     @property
-    def _is_aligned(self):
+    def _is_aligned(self) -> bool:
         return self.aligned_axes is not None and self.result_type is not None
 
-    @abc.abstractmethod
     def _evaluate(self):
         """
         Return an evaluated expression.
@@ -93,18 +93,19 @@ def _evaluate(self):
         -----
         Must be implemented by subclasses.
         """
-        pass
+        # mypy complains if we use @abc.abstractmethod, so we do use
+        #  AbstractMethodError instead
+        from pandas.errors import AbstractMethodError
+
+        raise AbstractMethodError(self)
 
 
 class NumExprEngine(AbstractEngine):
     """NumExpr engine class"""
 
     has_neg_frac = True
 
-    def __init__(self, expr):
-        super().__init__(expr)
-
-    def convert(self):
+    def convert(self) -> str:
         return str(super().convert())
 
     def _evaluate(self):
@@ -137,9 +138,6 @@ class PythonEngine(AbstractEngine):
 
     has_neg_frac = False
 
-    def __init__(self, expr):
-        super().__init__(expr)
-
     def evaluate(self):
         return self.expr()
 

pandas/core/computation/eval.py

@@ -15,7 +15,7 @@
 from pandas.io.formats.printing import pprint_thing
 
 
-def _check_engine(engine):
+def _check_engine(engine) -> str:
     """
     Make sure a valid engine is passed.
 
@@ -64,7 +64,7 @@ def _check_engine(engine):
     return engine
 
 
-def _check_parser(parser):
+def _check_parser(parser: str):
     """
     Make sure a valid parser is passed.
 
@@ -97,14 +97,13 @@ def _check_resolvers(resolvers):
                 )
 
 
-def _check_expression(expr):
+def _check_expression(expr: str):
     """
     Make sure an expression is not an empty string
 
     Parameters
     ----------
-    expr : object
-        An object that can be converted to a string
+    expr : str
 
     Raises
     ------
@@ -115,7 +114,7 @@ def _check_expression(expr):
         raise ValueError("expr cannot be an empty string")
 
 
-def _convert_expression(expr):
+def _convert_expression(expr) -> str:
     """
     Convert an object to an expression.
 
@@ -144,7 +143,7 @@ def _convert_expression(expr):
     return s
 
 
-def _check_for_locals(expr, stack_level, parser):
+def _check_for_locals(expr, stack_level: int, parser):
     from pandas.core.computation.expr import tokenize_string
 
     at_top_of_stack = stack_level == 0
@@ -168,15 +167,15 @@ def _check_for_locals(expr, stack_level, parser):
 
 def eval(
     expr,
-    parser="pandas",
+    parser: str = "pandas",
     engine=None,
     truediv=True,
     local_dict=None,
     global_dict=None,
     resolvers=(),
-    level=0,
+    level: int = 0,
     target=None,
-    inplace=False,
+    inplace: bool = False,
 ):
     """
     Evaluate a Python expression as a string using various backends.
@@ -192,7 +191,7 @@ def eval(
 
     Parameters
     ----------
-    expr : str or unicode
+    expr : str
         The expression to evaluate. This string cannot contain any Python
         `statements
         <https://docs.python.org/3/reference/simple_stmts.html#simple-statements>`__,
@@ -232,7 +231,7 @@ def eval(
         ``DataFrame.index`` and ``DataFrame.columns``
         variables that refer to their respective :class:`~pandas.DataFrame`
         instance attributes.
-    level : int, optional
+    level : int, default 0
         The number of prior stack frames to traverse and add to the current
         scope. Most users will **not** need to change this parameter.
     target : object, optional, default None

pandas/core/computation/expr.py

@@ -7,7 +7,7 @@
 import itertools as it
 import operator
 import tokenize
-from typing import Type
+from typing import Optional, Type
 
 import numpy as np
 
@@ -40,7 +40,7 @@
 import pandas.io.formats.printing as printing
 
 
-def tokenize_string(source):
+def tokenize_string(source: str):
     """
     Tokenize a Python source code string.
 
@@ -68,7 +68,8 @@ def tokenize_string(source):
 
 
 def _rewrite_assign(tok):
-    """Rewrite the assignment operator for PyTables expressions that use ``=``
+    """
+    Rewrite the assignment operator for PyTables expressions that use ``=``
     as a substitute for ``==``.
 
     Parameters
@@ -86,7 +87,8 @@ def _rewrite_assign(tok):
 
 
 def _replace_booleans(tok):
-    """Replace ``&`` with ``and`` and ``|`` with ``or`` so that bitwise
+    """
+    Replace ``&`` with ``and`` and ``|`` with ``or`` so that bitwise
     precedence is changed to boolean precedence.
 
     Parameters
@@ -110,7 +112,8 @@ def _replace_booleans(tok):
 
 
 def _replace_locals(tok):
-    """Replace local variables with a syntactically valid name.
+    """
+    Replace local variables with a syntactically valid name.
 
     Parameters
     ----------
@@ -135,7 +138,8 @@ def _replace_locals(tok):
 
 
 def _clean_spaces_backtick_quoted_names(tok):
-    """Clean up a column name if surrounded by backticks.
+    """
+    Clean up a column name if surrounded by backticks.
 
     Backtick quoted string are indicated by a certain tokval value. If a string
     is a backtick quoted token it will processed by
@@ -303,7 +307,8 @@ def f(self, *args, **kwargs):
 
 
 def disallow(nodes):
-    """Decorator to disallow certain nodes from parsing. Raises a
+    """
+    Decorator to disallow certain nodes from parsing. Raises a
     NotImplementedError instead.
 
     Returns
@@ -324,16 +329,17 @@ def disallowed(cls):
 
 
 def _op_maker(op_class, op_symbol):
-    """Return a function to create an op class with its symbol already passed.
+    """
+    Return a function to create an op class with its symbol already passed.
 
     Returns
     -------
     f : callable
     """
 
     def f(self, node, *args, **kwargs):
-        """Return a partial function with an Op subclass with an operator
-        already passed.
+        """
+        Return a partial function with an Op subclass with an operator already passed.
 
         Returns
         -------
@@ -813,18 +819,27 @@ class Expr:
     parser : str, optional, default 'pandas'
     env : Scope, optional, default None
     truediv : bool, optional, default True
-    level : int, optional, default 2
+    level : int, optional, default 0
     """
 
     def __init__(
-        self, expr, engine="numexpr", parser="pandas", env=None, truediv=True, level=0
+        self,
+        expr,
+        engine: str = "numexpr",
+        parser: str = "pandas",
+        env=None,
+        truediv: bool = True,
+        level: int = 0,
     ):
         self.expr = expr
         self.env = env or Scope(level=level + 1)
         self.engine = engine
         self.parser = parser
         self.env.scope["truediv"] = truediv
-        self._visitor = _parsers[parser](self.env, self.engine, self.parser)
+        self._visitor = _parsers[parser](
+            self.env, self.engine, self.parser
+        )  # type: Optional[BaseExprVisitor]
+        assert isinstance(self._visitor, BaseExprVisitor), type(self._visitor)
         self.terms = self.parse()
 
     @property
@@ -834,10 +849,10 @@ def assigner(self):
     def __call__(self):
         return self.terms(self.env)
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return printing.pprint_thing(self.terms)
 
-    def __len__(self):
+    def __len__(self) -> int:
         return len(self.expr)
 
     def parse(self):

pandas/core/computation/expressions.py

@@ -157,7 +157,7 @@ def _where_numexpr(cond, a, b):
 set_use_numexpr(get_option("compute.use_numexpr"))
 
 
-def _has_bool_dtype(x):
+def _has_bool_dtype(x) -> bool:
     if isinstance(x, ABCDataFrame):
         return "bool" in x.dtypes
     try: