CLN: Use generators in builtin functions (pandas-dev#19989)

Author: mroeschke

pandas/_libs/parsers.pyx

@@ -1045,7 +1045,7 @@ cdef class TextReader:
                 usecols = set()
                 if callable(self.usecols):
                     if self.usecols(name):
-                        usecols = set([i])
+                        usecols = {i}
                 else:
                     usecols = self.usecols
                 if self.has_usecols and not (i in usecols or

pandas/_libs/tslibs/parsing.pyx

@@ -57,7 +57,7 @@ _DEFAULT_DATETIME = datetime(1, 1, 1).replace(hour=0, minute=0,
 
 cdef object _TIMEPAT = re.compile(r'^([01]?[0-9]|2[0-3]):([0-5][0-9])')
 
-cdef set _not_datelike_strings = set(['a', 'A', 'm', 'M', 'p', 'P', 't', 'T'])
+cdef set _not_datelike_strings = {'a', 'A', 'm', 'M', 'p', 'P', 't', 'T'}
 
 NAT_SENTINEL = object()
 # This allows us to reference NaT without having to import it
@@ -651,7 +651,7 @@ def _guess_datetime_format(dt_str, dayfirst=False, dt_str_parse=du_parse,
                     break
 
     # Only consider it a valid guess if we have a year, month and day
-    if len(set(['year', 'month', 'day']) & found_attrs) != 3:
+    if len({'year', 'month', 'day'} & found_attrs) != 3:
         return None
 
     output_format = []

pandas/compat/pickle_compat.py

@@ -38,9 +38,9 @@ def load_reduce(self):
 
         # try to re-encode the arguments
         if getattr(self, 'encoding', None) is not None:
-            args = tuple([arg.encode(self.encoding)
-                          if isinstance(arg, string_types)
-                          else arg for arg in args])
+            args = tuple(arg.encode(self.encoding)
+                         if isinstance(arg, string_types)
+                         else arg for arg in args)
             try:
                 stack[-1] = func(*args)
                 return

pandas/core/generic.py

@@ -212,9 +212,8 @@ def _dir_additions(self):
         """ add the string-like attributes from the info_axis.
         If info_axis is a MultiIndex, it's first level values are used.
         """
-        additions = set(
-            [c for c in self._info_axis.unique(level=0)[:100]
-             if isinstance(c, string_types) and isidentifier(c)])
+        additions = {c for c in self._info_axis.unique(level=0)[:100]
+                     if isinstance(c, string_types) and isidentifier(c)}
         return super(NDFrame, self)._dir_additions().union(additions)
 
     @property

pandas/core/indexing.py

@@ -905,9 +905,8 @@ def _multi_take(self, tup):
         """
         try:
             o = self.obj
-            d = dict(
-                [(a, self._convert_for_reindex(t, axis=o._get_axis_number(a)))
-                 for t, a in zip(tup, o._AXIS_ORDERS)])
+            d = {a: self._convert_for_reindex(t, axis=o._get_axis_number(a))
+                 for t, a in zip(tup, o._AXIS_ORDERS)}
             return o.reindex(**d)
         except(KeyError, IndexingError):
             raise self._exception