在python中格式化一个异常,包括除最后一个'n'回溯帧之外的所有异常

Question

假设您有这样的设置:

def a():
    b()

def b():
    c()

def c():
    d()

def d():
    e()

尝试调用a()将导致以下回溯:

Traceback (most recent call last):
  File "<pyshell#181>", line 1, in <module>
    a()
  File "<pyshell#87>", line 2, in a
    b()
  File "<pyshell#90>", line 2, in b
    c()
  File "<pyshell#93>", line 2, in c
    d()
  File "<pyshell#96>", line 2, in d
    e()
NameError: name 'e' is not defined

有没有办法格式化异常,以便它只包括n回溯中的最后一帧？例如,如果n = 2,traceback将如下所示:

Traceback (most recent call last):
  File "<pyshell#93>", line 2, in c
    d()
  File "<pyshell#96>", line 2, in d
    e()
NameError: name 'e' is not defined

我已经对它进行了一点点修改,无法想出办法.

Answer 1

从Python 3.5开始,追溯模块的功能支持负面限制(原始提案受到您的问题的启发并经Guido批准):

import traceback

n = 2

try:
    a()
except:
    traceback.print_exc(limit=-n) # `n` last traceback entries

输出

Traceback (most recent call last):
  File "/home/vaultah/test.py", line 8, in c
    d()
  File "/home/vaultah/test.py", line 11, in d
    e()
NameError: name 'e' is not defined

即使您使用较旧的Python,也可以复制此行为

import sys, traceback

n = 2

try:
    a()
except:
    ex = traceback.format_exception(*sys.exc_info())
    sys.stderr.write(''.join([ex[0]] + ex[-n-1:]))
    # or print(*[ex[0]] + ex[-n-1:], sep='', end='', file=sys.stderr)

输出将完全相同.