Implement suggestions from code review.

- Avoid importing numpy unless necessary.

- Mention numpy arrays and dictionaries in the docs.

- Add numpy to the list of tox dependencies.

- Don't unnecessarily copy arrays or allocate empty space for them.

- Use code from compat.py rather than writing py2/3 versions of things
  myself.

- Avoid reimplementing __repr__ for built-in types.

- Add an option to consider NaN == NaN, because sometimes people use NaN
  to mean "missing data".

Author: kalekundert

_pytest/compat.py

@@ -125,6 +125,7 @@ def isclass(object):
 if _PY3:
     import codecs
     imap = map
+    izip = zip
     STRING_TYPES = bytes, str
     UNICODE_TYPES = str,
 
@@ -160,7 +161,7 @@ def _escape_strings(val):
     STRING_TYPES = bytes, str, unicode
     UNICODE_TYPES = unicode,
 
-    from itertools import imap  # NOQA
+    from itertools import imap, izip  # NOQA
 
     def _escape_strings(val):
         """In py2 bytes and str are the same type, so return if it's a bytes