TST: Rework style test skip

Also redoes some of the changes that were inadvertently revereted
in #12260.

That PR had two commits, one of which was an older version of
what was eventually merged in
#12162.

The stale commit incorrectly merged was a15248a.
It should have been a3c38fe.

For the most part the changes were just style, but there was a python2
import error, which our tests didn't fail on because I was trying to
catch a jinja ImportError, and instead caught all ImportErrors.

Author: TomAugspurger

pandas/core/style.py

@@ -7,8 +7,7 @@
 from contextlib import contextmanager
 from uuid import uuid1
 import copy
-from collections import defaultdict
-from collections.abc import MutableMapping
+from collections import defaultdict, MutableMapping
 
 try:
     from jinja2 import Template
@@ -273,7 +272,7 @@ def _translate(self):
                     caption=caption, table_attributes=self.table_attributes)
 
     def format(self, formatter, subset=None):
-        '''
+        """
         Format the text display value of cells.
 
         .. versionadded:: 0.18.0
@@ -282,6 +281,8 @@ def format(self, formatter, subset=None):
         ----------
         formatter: str, callable, or dict
         subset: IndexSlice
+            An argument to ``DataFrame.loc`` that restricts which elements
+            ``formatter`` is applied to.
 
         Returns
         -------
@@ -292,8 +293,9 @@ def format(self, formatter, subset=None):
 
         ``formatter`` is either an ``a`` or a dict ``{column name: a}`` where
         ``a`` is one of
-            - str: this will be wrapped in: ``a.format(x)``
-            - callable: called with the value of an individual cell
+
+        - str: this will be wrapped in: ``a.format(x)``
+        - callable: called with the value of an individual cell
 
         The default display value for numeric values is the "general" (``g``)
         format with ``pd.options.display.precision`` precision.
@@ -305,7 +307,7 @@ def format(self, formatter, subset=None):
         >>> df.style.format("{:.2%}")
         >>> df['c'] = ['a', 'b', 'c', 'd']
         >>> df.style.format({'C': str.upper})
-        '''
+        """
         if subset is None:
             row_locs = range(len(self.data))
             col_locs = range(len(self.data.columns))
@@ -853,11 +855,11 @@ def _highlight_extrema(data, color='yellow', max_=True):
 
 
 def _maybe_wrap_formatter(formatter):
-    if not (callable(formatter) or com.is_string_like(formatter)):
+    if com.is_string_like(formatter):
+        return lambda x: formatter.format(x)
+    elif callable(formatter):
+        return formatter
+    else:
         msg = "Expected a template string or callable, got {} instead".format(
             formatter)
         raise TypeError(msg)
-    if not callable(formatter):
-        return lambda x: formatter.format(x)
-    else:
-        return formatter

pandas/tests/test_style.py

@@ -17,9 +17,12 @@
 if job_name == '27_slow_nnet_LOCALE':
     raise SkipTest("No jinja")
 try:
-    from pandas.core.style import Styler
+    # Do try except on just jinja, so the only reason
+    # We skip is if jinja can't import, not something else
+    import jinja2  # noqa
 except ImportError:
     raise SkipTest("No Jinja2")
+from pandas.core.style import Styler  # noqa
 
 
 class TestStyler(TestCase):