python traceback class_traceback：让你更加灵活地处理python的异常
異常
異常在python中是屢見不鮮了，程序在執行到某一行代碼時，發現有問題，比如數組索引越界，變量沒有定義啊等等，此時就會拋出異常
捕獲異常
在python，一般都是使用try···except來對異常進行捕獲
python
try:
1 / 0
except Exception as e:
print(e) # division by zero
然而僅僅只有這些也看不出什么東西來，我們需要知道在哪一行代碼引發的異常。
大家在程序報錯的時候，會經常看到報錯信息如下
Traceback (most recent call last):
這個Traceback是什么鬼？實際上，這是python關于程序報錯的回溯信息，來自于一個叫做traceback object的對象，而這個traceback object對象是通過sys.exc_info()來獲取的
traceback對象
python
import sys
try:
1 / 0
except Exception as e:
print(e) # division by zero
exc_type, exc_value, exc_tb = sys.exc_info()
print(exc_type) #
print(exc_value) # division by zero
print(exc_tb) #
可以看到，sys.exc_info()獲取了當前處理的exception的相關信息，并返回一個元組。元組的第一個元素是異常的類型，第二個元素是異常的value值，第三個異常信息則是traceback object。print(e)打印的是異常的值。
有了traceback object我們則可以打印和格式化traceback的相關信息
traceback模塊
print_tb
接收一個tracebackobject
python
import sys
import traceback
try:
1 / 0
except NameError as e:
exc_type, exc_value, exc_tb = sys.exc_info()
traceback.print_tb(exc_tb)
"""
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 6, in
1 / 0
"""
# 如果我們不捕獲異常看看輸出啥？
"""
Traceback (most recent call last):
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 6, in
1 / 0
ZeroDivisionError: division by zero
"""
# 可以看到最后一行的ZeroDivisionError則是異常類型，division by zero則是異常值。中間的則是我們的traceback object
然而除了traceback object，print_tb還可以接收兩個參數
limit
比如我們在調用C函數出現了異常，但我們是先調用A函數，在A函數里面調用B函數，在B函數里面調用C函數，limit參數則是限制stack trace的層級的，如果為None也就是不指定，那么會打印所有層級
python
import sys
import traceback
defC():
1 / 0
defB():
C()
defA():
B()
try:
A()
except Exception as e:
exc_type, exc_value, exc_tb = sys.exc_info()
traceback.print_tb(exc_tb)
"""
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 16, in
A()
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 12, in A
B()
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 9, in B
C()
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 6, in C
1 / 0
"""
traceback.print_tb(exc_tb, limit=2)
"""
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 16, in
A()
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 12, in A
B()
"""
file
可以指定file，輸出到某個文件里，默認是sys.stderr
print_exception
與print_tb相比多了兩個參數，需要傳入exc_type,exc_value,exc_tb，也就是sys.exc_info返回的三個值。與print_tb相比，打印信息多了開頭的Traceback (most recent call last):，以及最后一行的異常類型和value信息。還有一個不同是當異常為SyntaxError時，會有"^"來指示語法錯誤的位置
python
import sys
import traceback
defC():
1 / 0
defB():
C()
defA():
B()
try:
A()
except Exception as e:
exc_type, exc_value, exc_tb = sys.exc_info()
traceback.print_exception(exc_type, exc_value, exc_tb)
"""
Traceback (most recent call last):
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 16, in
A()
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 12, in A
B()
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 9, in B
C()
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 6, in C
1 / 0
ZeroDivisionError: division by zero
"""
可以看到，打印的結果和報錯的信息是一樣的。
print_exc
和print_exception類似，只不過不需要我們手動的傳入sys.exc_info返回的三個值，而是會自動幫我們調用
python
import sys
import traceback
defC():
1 / 0
defB():
C()
defA():
B()
try:
A()
except Exception as e:
traceback.print_exc()
"""
Traceback (most recent call last):
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 16, in
A()
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 12, in A
B()
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 9, in B
C()
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 6, in C
1 / 0
ZeroDivisionError: division by zero
"""
format_exc
和print_exc一樣，只不過是以字符串的形式返回，需要我們自己手動打印
python
import sys
import traceback
defC():
1 / 0
defB():
C()
defA():
B()
try:
A()
except Exception as e:
tb_info = traceback.format_exc()
print(tb_info)
"""
Traceback (most recent call last):
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 16, in
A()
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 12, in A
B()
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 9, in B
C()
File "C:/Users/EDZ/Desktop/satori/wtfpython/1.py", line 6, in C
1 / 0
ZeroDivisionError: division by zero
"""
總結
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