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      1 # Copyright (c) 2014 The Chromium Authors. All rights reserved.
      2 # Use of this source code is governed by a BSD-style license that can be
      3 # found in the LICENSE file.
      4 
      5 # This module contains some commonly used time conversion function.
      6 
      7 import datetime
      8 import time
      9 
     10 
     11 # This format is used to parse datetime value in MySQL database and should not
     12 # be modified.
     13 TIME_FMT = '%Y-%m-%d %H:%M:%S'
     14 TIME_FMT_MICRO = '%Y-%m-%d %H:%M:%S.%f'
     15 
     16 def time_string_to_datetime(time_string, handle_type_error=False):
     17     """Convert a string of time to a datetime object.
     18 
     19     The format of date string must match '%Y-%m-%d %H:%M:%S' or
     20     '%Y-%m-%d %H:%M:%S.%f'.
     21 
     22     @param time_string: String of date, e.g., 2014-12-05 15:32:45
     23     @param handle_type_error: Set to True to prevent the method raise
     24             TypeError if given time_string is corrupted. Default is False.
     25 
     26     @return: A datetime object with time of the given date string.
     27 
     28     """
     29     try:
     30         try:
     31             return datetime.datetime.strptime(time_string, TIME_FMT)
     32         except ValueError:
     33             return datetime.datetime.strptime(time_string, TIME_FMT_MICRO)
     34     except TypeError:
     35         if handle_type_error:
     36             return None
     37         else:
     38             raise
     39 
     40 
     41 def date_string_to_epoch_time(date_string):
     42     """Parse a date time string into seconds since the epoch.
     43 
     44     @param date_string: A string, formatted according to `TIME_FMT`.
     45 
     46     @return The number of seconds since the UNIX epoch, as a float.
     47 
     48     """
     49     return time.mktime(time.strptime(date_string, TIME_FMT))
     50 
     51 
     52 def epoch_time_to_date_string(epoch_time, fmt_string=TIME_FMT):
     53     """Convert epoch time (float) to a human readable date string.
     54 
     55     @param epoch_time The number of seconds since the UNIX epoch, as
     56                       a float.
     57     @param fmt_string: A string describing the format of the datetime
     58         string output.
     59 
     60     @returns: string formatted in the following way: "yyyy-mm-dd hh:mm:ss"
     61     """
     62     if epoch_time:
     63         return datetime.datetime.fromtimestamp(
     64                 int(epoch_time)).strftime(fmt_string)
     65     return None
     66 
     67 
     68 def to_epoch_time(value):
     69     """Convert the given value to epoch time.
     70 
     71     Convert the given value to epoch time if it is a datetime object or a string
     72     can be converted to datetime object.
     73     If the given value is a number, this function assume the value is a epoch
     74     time value, and returns the value itself.
     75 
     76     @param value: A datetime object or a number.
     77     @returns: epoch time if value is datetime.datetime,
     78               otherwise returns the value.
     79     @raise ValueError: If value is not a datetime object or a number.
     80     """
     81     if isinstance(value, basestring):
     82         value = time_string_to_datetime(value)
     83     if isinstance(value, datetime.datetime):
     84         return time.mktime(value.timetuple()) + 0.000001 * value.microsecond
     85     if not isinstance(value, int) and not isinstance(value, float):
     86         raise ValueError('Value should be a datetime object, string or a '
     87                          'number. Unexpected value: %s.' % value)
     88     return value
     89