Python关于try语句需要注意的几点

try语句属于防御性编程的一种，允许我们捕获异常进行处理，提高程序的健壮性。

在 finally 块中不管你在 except 中是否抛出异常都会执行，如下：

def f():try:print("try")a = 0 /0except Exception as e:print("except")raise efinally:print("finally")return "return"
print(f())

try
except
finally
Traceback (most recent call last):File "/Users/birenjianmo/.vscode/extensions/ms-python.python-2019.3.6558/pythonFiles/ptvsd_launcher.py", line 45, in <module>main(ptvsdArgs)File "/Users/birenjianmo/.vscode/extensions/ms-python.python-2019.3.6558/pythonFiles/lib/python/ptvsd/__main__.py", line 391, in mainrun()File "/Users/birenjianmo/.vscode/extensions/ms-python.python-2019.3.6558/pythonFiles/lib/python/ptvsd/__main__.py", line 272, in run_filerunpy.run_path(target, run_name='__main__')File "/Users/birenjianmo/anaconda3/lib/python3.6/runpy.py", line 263, in run_pathpkg_name=pkg_name, script_name=fname)File "/Users/birenjianmo/anaconda3/lib/python3.6/runpy.py", line 96, in _run_module_codemod_name, mod_spec, pkg_name, script_name)File "/Users/birenjianmo/anaconda3/lib/python3.6/runpy.py", line 85, in _run_codeexec(code, run_globals)File "/Users/birenjianmo/Desktop/learn/pyzbar/test6.py", line 11, in <module>print(f())File "/Users/birenjianmo/Desktop/learn/pyzbar/test6.py", line 7, in fraise eFile "/Users/birenjianmo/Desktop/learn/pyzbar/test6.py", line 4, in fa = 0 /0
ZeroDivisionError: division by zero

而如果你在 finally 块中使用 return 关键字，则不会执行 except 中 raise，也就是说不能在 except 抛出异常

def f():try:print("try")a = 0 /0except Exception as e:print("except")raise efinally:print("finally")return "return"
print(f())

try
except
finally
return

 而不管程序没有报错，在 try 或 except 中 return 或 raise 之前会先执行 finally，但是如果 return 或 raise 一个方法时，会先执行右边的方法。

def f():try:print("try")# a = 0 /0return "return - try"except Exception as e:print("except")raise efinally:print("finally")return "return"
print(f())

try
finally
return

def _f():print("_f")return "_f return"def f():try:print("try")# a = 0 /0return _f()except Exception as e:print("except")raise efinally:print("finally")return "return"
print(f())

try
_f
finally
return