Python常见问题解答：“异常有多快？”

捕获异常 非常 昂贵，但是异常应该是 例外的 （读取，不经常发生）。如果例外情况很少，

try/catch

下面的示例在密钥存在和不存在时使用异常和LBYL对字典密钥进行计时：

import timeits = []s.append('''try:    x = D['key']except KeyError:    x = None''')s.append('''x = D['key'] if 'key' in D else None''')s.append('''try:    x = D['xxx']except KeyError:    x = None''')s.append('''x = D['xxx'] if 'xxx' in D else None''')for i,c in enumerate(s,1):    t = timeit.Timer(c,"D={'key':'value'}")    print('Run',i,'=',min(t.repeat()))

输出量

Run 1 = 0.05600167960596991       # try/catch, key existsRun 2 = 0.08530091918578364       # LBYL, key exists (slower)Run 3 = 0.3486251291120652        # try/catch, key doesn't exist (MUCH slower)Run 4 = 0.050621117060586585      # LBYL, key doesn't exist

当通常情况也不例外

try/catch