python中测量时间的异常结果
这是我的秒表课python中测量时间的异常结果,python,performance,time,Python,Performance,Time,这是我的秒表课 import time class StopWatch: def __init__(self, tag="", startTime=time.time(), elapsedTime=-1): self._tag=tag self._elapsedTime=elapsedTime self._startTime=startTime # other codes here............# def
import time
class StopWatch:
def __init__(self, tag="", startTime=time.time(), elapsedTime=-1):
self._tag=tag
self._elapsedTime=elapsedTime
self._startTime=startTime
# other codes here............#
def stop(self, tag=None):
if tag is not None:
self._tag = tag
self._elapsedTime = time.time() - self._startTime
return self
def getStartTime(self):
return self._startTime
秒表测试文件为:import unittest
import time
from metric.StopWatch import StopWatch
class StopWatchTest(unittest.TestCase):
def test_stopwatch(self):
now=time.time()
print "now:%f" % now
stopwatch=StopWatch("firstHook")
print "start time:%r" % stopwatch.getStartTime()
self.assertTrue(stopwatch.getStartTime()>now, "start time is wrong")
我得到的是错误:
now:1364791630.047630
start time:1364791629.158797
稍后执行的代码显示的是较早的时间。这背后的原因是什么?原因是这一行:
def __init__(self, tag="", startTime=time.time(), elapsedTime=-1):
当Python解释器到达时对其进行计算(因为尽管名称不同,它实际上编译代码,尽管是字节码)。因此,startTime是在定义类时设置的,而不是在调用\uuuu init\uuuu
时设置的
将其更改为:
def __init__(self, tag="", start_time=None, elapsed_time=-1):
if start_time is None:
start_time = time.time()
self._tag=tag
self._elapsed_time=elapsed_Time
self._start_time=start_time
原因是这一行:
def __init__(self, tag="", startTime=time.time(), elapsedTime=-1):
当Python解释器到达时对其进行计算(因为尽管名称不同,它实际上编译代码,尽管是字节码)。因此,startTime是在定义类时设置的,而不是在调用\uuuu init\uuuu
时设置的
将其更改为:
def __init__(self, tag="", start_time=None, elapsed_time=-1):
if start_time is None:
start_time = time.time()
self._tag=tag
self._elapsed_time=elapsed_Time
self._start_time=start_time
默认参数只计算一次
def __init__(self, tag="", startTime=time.time(), elapsedTime=-1):
self._tag=tag
self._elapsedTime = elapsedTime
self._startTime = startTime
要修复此问题,我们需要明确检查默认值,并在函数体中对其求值:
def __init__(self, tag="", startTime=None, elapsedTime=-1):
self._tag=tag
self._elapsedTime = elapsedTime
if startTime is None:
startTime = time.time()
self._startTime = startTime
默认参数只计算一次
def __init__(self, tag="", startTime=time.time(), elapsedTime=-1):
self._tag=tag
self._elapsedTime = elapsedTime
self._startTime = startTime
要修复此问题,我们需要明确检查默认值,并在函数体中对其求值:
def __init__(self, tag="", startTime=None, elapsedTime=-1):
self._tag=tag
self._elapsedTime = elapsedTime
if startTime is None:
startTime = time.time()
self._startTime = startTime