Fix performance regression from version 4.0.0 (#386)

* Fix performance issue when collecting tests.

* Add changelog entry

CHANGES.rst

@@ -1,6 +1,11 @@
 Changelog
 =========
 
+Unreleased
+----------
+- Fixed performance regression introduced in 4.0.0 where collection time of tests would take way longer than before. (youtux)
+
+
 4.0.0
 -----
 

pytest_bdd/utils.py

@@ -1,29 +1,39 @@
 """Various utility functions."""
 
-import inspect
+from sys import _getframe
+from inspect import getframeinfo
 
 import six
 
 CONFIG_STACK = []
 
+if six.PY2:
+    from inspect import getargspec as _getargspec
 
-def get_args(func):
-    """Get a list of argument names for a function.
+    def get_args(func):
+        """Get a list of argument names for a function.
 
-    This is a wrapper around inspect.getargspec/inspect.signature because
-    getargspec got deprecated in Python 3.5 and signature isn't available on
-    Python 2.
+        :param func: The function to inspect.
 
-    :param func: The function to inspect.
+        :return: A list of argument names.
+        :rtype: list
+        """
+        return _getargspec(func).args
 
-    :return: A list of argument names.
-    :rtype: list
-    """
-    if six.PY2:
-        return inspect.getargspec(func).args
 
-    params = inspect.signature(func).parameters.values()
-    return [param.name for param in params if param.kind == param.POSITIONAL_OR_KEYWORD]
+else:
+    from inspect import signature as _signature
+
+    def get_args(func):
+        """Get a list of argument names for a function.
+
+        :param func: The function to inspect.
+
+        :return: A list of argument names.
+        :rtype: list
+        """
+        params = _signature(func).parameters.values()
+        return [param.name for param in params if param.kind == param.POSITIONAL_OR_KEYWORD]
 
 
 def get_parametrize_markers_args(node):
@@ -36,11 +46,19 @@ def get_parametrize_markers_args(node):
 
 
 def get_caller_module_locals(depth=2):
-    frame_info = inspect.stack()[depth]
-    frame = frame_info[0]  # frame_info.frame
-    return frame.f_locals
+    """Get the caller module locals dictionary.
+
+    We use sys._getframe instead of inspect.stack(0) because the latter is way slower, since it iterates over
+    all the frames in the stack.
+    """
+    return _getframe(depth).f_locals
 
 
 def get_caller_module_path(depth=2):
-    frame_info = inspect.stack()[depth]
-    return frame_info[1]  # frame_info.filename
+    """Get the caller module path.
+
+    We use sys._getframe instead of inspect.stack(0) because the latter is way slower, since it iterates over
+    all the frames in the stack.
+    """
+    frame = _getframe(depth)
+    return getframeinfo(frame, context=0).filename