如何在Python函數執行前后增加額外的行為

from functools import wraps, partial
from time import time

def timing(func=None, frequencies=1):
 if func is None:
 # print("+None")
 return partial(timing, frequencies=frequencies)
 # else:
 # print("-None")

 @wraps(func)
 def _wrapper(*args, **kwargs):
 start_time = time()
 for t in range(frequencies):
 result = func(*args, **kwargs)
 end_time = time()
 print('運行花費時間：{:.6f}s。'.format(end_time-start_time))
 return result

 return _wrapper


@timing
def run():
 l = []
 for i in range(5000000):
 l.extend([i])
 return len(l)

In [4]: run()
運行花費時間：2.383398s。
Out[4]: 5000000

from time import time

def run2():
 l = []
 for i in range(5000000):
 l.extend([i])
 return len(l)

class ElapsedTime():
 def __enter__(self):
 self.start_time = time()
 return self

 def __exit__(self, exception_type, exception_value, traceback):
 self.end_time = time()
 print('運行花費時間：{:.6f}s。'.format(self.end_time - self.start_time))

with ElapsedTime():
 run2()