Switch to monotonic clock for timers (#13)

humanfriendly/__init__.py

@@ -1,7 +1,7 @@
 # Human friendly input/output in Python.
 #
 # Author: Peter Odding <peter@peterodding.com>
-# Last Change: January 10, 2017
+# Last Change: January 16, 2017
 # URL: https://humanfriendly.readthedocs.io
 
 """The main module of the `humanfriendly` package."""
@@ -36,7 +36,7 @@
 from humanfriendly.prompts import prompt_for_choice  # NOQA
 
 # Compatibility with Python 2 and 3.
-from humanfriendly.compat import is_string
+from humanfriendly.compat import is_string, monotonic
 
 # Semi-standard module versioning.
 __version__ = '2.2.1'
@@ -581,13 +581,23 @@ def __init__(self, start_time=None, resumable=False):
 
         :param start_time: The start time (a float, defaults to the current time).
         :param resumable: Create a resumable timer (defaults to :data:`False`).
+
+        When `start_time` is given :class:`Timer` uses :func:`time.time()` as a
+        clock source, otherwise it uses :func:`humanfriendly.compat.monotonic()`.
         """
-        self.resumable = resumable
-        if self.resumable:
+        if resumable:
+            self.monotonic = True
+            self.resumable = True
             self.start_time = 0.0
             self.total_time = 0.0
+        elif start_time:
+            self.monotonic = False
+            self.resumable = False
+            self.start_time = start_time
         else:
-            self.start_time = start_time or time.time()
+            self.monotonic = True
+            self.resumable = False
+            self.start_time = monotonic()
 
     def __enter__(self):
         """
@@ -598,7 +608,7 @@ def __enter__(self):
         """
         if not self.resumable:
             raise ValueError("Timer is not resumable!")
-        self.start_time = time.time()
+        self.start_time = monotonic()
         return self
 
     def __exit__(self, exc_type=None, exc_value=None, traceback=None):
@@ -609,8 +619,9 @@ def __exit__(self, exc_type=None, exc_value=None, traceback=None):
         """
         if not self.resumable:
             raise ValueError("Timer is not resumable!")
-        self.total_time += time.time() - self.start_time
-        self.start_time = 0
+        if self.start_time:
+            self.total_time += monotonic() - self.start_time
+            self.start_time = 0.0
 
     @property
     def elapsed_time(self):
@@ -621,7 +632,8 @@ def elapsed_time(self):
         if self.resumable:
             elapsed_time += self.total_time
         if self.start_time:
-            elapsed_time += time.time() - self.start_time
+            current_time = monotonic() if self.monotonic else time.time()
+            elapsed_time += current_time - self.start_time
         return elapsed_time
 
     @property

humanfriendly/compat.py

@@ -1,7 +1,7 @@
 # Human friendly input/output in Python.
 #
 # Author: Peter Odding <peter@peterodding.com>
-# Last Change: September 28, 2016
+# Last Change: January 16, 2017
 # URL: https://humanfriendly.readthedocs.io
 
 """
@@ -29,20 +29,50 @@
 
    Alias for :func:`python2:unicode` (in Python 2) or :class:`python3:str` (in
    Python 3). See also :func:`coerce_string()`.
+
+.. data:: monotonic
+
+   Alias for :func:`python3:time.monotonic()` (in Python 3.3 and higher) or
+   `monotonic.monotonic()` (a `conditional dependency
+   <https://pypi.python.org/pypi/monotonic/>`_ on older Python versions).
 """
 
+__all__ = (
+    'StringIO',
+    'basestring',
+    'coerce_string',
+    'interactive_prompt',
+    'is_string',
+    'is_unicode',
+    'monotonic',
+    'unicode',
+)
+
 try:
     # Python 2.
     unicode = unicode
     basestring = basestring
-    interactive_prompt = raw_input  # NOQA
+    interactive_prompt = raw_input
     from StringIO import StringIO
 except (ImportError, NameError):
     # Python 3.
     unicode = str
     basestring = str
     interactive_prompt = input
-    from io import StringIO  # NOQA
+    from io import StringIO
+
+try:
+    # Python 3.3 and higher.
+    from time import monotonic
+except ImportError:
+    # A replacement for older Python versions:
+    # https://pypi.python.org/pypi/monotonic/
+    try:
+        from monotonic import monotonic
+    except (ImportError, RuntimeError):
+        # We fall back to the old behavior of using time.time() instead of
+        # failing when {time,monotonic}.monotonic() are both missing.
+        from time import time as monotonic
 
 
 def coerce_string(value):

setup.py

@@ -47,15 +47,30 @@ def get_install_requires():
     install_requires = []
     if sys.version_info[:2] <= (2, 6) or sys.version_info[:2] == (3, 0):
         install_requires.append('importlib')
-    return install_requires
+    if sys.version_info[:2] < (3, 3):
+        install_requires.append('monotonic')
+    return sorted(install_requires)
 
 
 def get_extras_require():
     """Add conditional dependencies for Python 2 (when creating wheel distributions)."""
     extras_require = {}
     if have_environment_marker_support():
-        expression = ':python_version == "2.6" or python_version == "3.0"'
+        # Conditional `importlib' dependency.
+        expression = ':%s' % ' or '.join([
+            'python_version == "2.6"',
+            'python_version == "3.0"',
+        ])
         extras_require[expression] = ['importlib']
+        # Conditional `monotonic' dependency.
+        expression = ':%s' % ' or '.join([
+            'python_version == "2.6"',
+            'python_version == "2.7"',
+            'python_version == "3.0"',
+            'python_version == "3.1"',
+            'python_version == "3.2"',
+        ])
+        extras_require[expression] = ['monotonic']
     return extras_require