python try catch finally执行顺序_对python中的try、except、finally 执行顺序详解
如下所示:
def test1():
try:
print('to do stuff')
raise Exception('hehe')
print('to return in try')
return 'try'
except Exception:
print('process except')
print('to return in except')
return 'except'
finally:
print('to return in finally')
return 'finally'
test1Return = test1()
print('test1Return : ' + test1Return)
輸出:
to do stuff
process except
to return in except
to return in finally
test1Return : finally
在 try 中 raise一個異常,就立刻轉(zhuǎn)入 except 中執(zhí)行,在except 中遇到 return 時,就強制轉(zhuǎn)到 finally 中執(zhí)行, 在 finally 中遇到 return 時就返回
def test2():
try:
print('to do stuff')
print('to return in try')
return 'try'
except Exception:
print('process except')
print('to return in except')
return 'except'
finally:
print('to return in finally')
return 'finally'
test2Return = test2()
print('test1Return : ' + test2Return)
輸出:
to do stuff
to return in try
to return in finally
test2Return : finally
這里在 try 中沒有拋出異常,因此不會轉(zhuǎn)到 except 中,但是在try 中遇到return時,也會立即強制轉(zhuǎn)到finally中執(zhí)行,并在finally中返回
test1和test2得到的結(jié)論:
無論是在try還是在except中,遇到return時,只要設(shè)定了finally語句,就會中斷當前的return語句,跳轉(zhuǎn)到finally中執(zhí)行,如果finally中遇到return語句,就直接返回,不再跳轉(zhuǎn)回try/excpet中被中斷的return語句
def test3():
i = 0
try:
i += 1
print('i in try : %s'%i)
raise Exception('hehe')
except Exception:
i += 1
print('i in except : %s'%i)
return i
finally:
i += 1
print ('i in finally : %s'%i )
print('test3Return : %s'% test3())
輸出:
i in try : 1
i in except : 2
i in finally : 3
test3Return : 2
def test4():
i = 0
try:
i += 1
return i
finally:
i += 1
print ('i in finally : %s'%i )
print('test4Return : %s' % test4())
輸出
i in finally : 2
test4Return : 1
test3和test4得到的結(jié)論:
在except和try中遇到return時,會鎖定return的值,然后跳轉(zhuǎn)到finally中,如果finally中沒有return語句,則finally執(zhí)行完畢之后仍返回原return點,將之前鎖定的值返回(即finally中的動作不影響返回值),如果finally中有return語句,則執(zhí)行finally中的return語句。
def test5():
for i in range(5):
try:
print('do stuff %s'%i)
raise Exception(i)
except Exception:
print('exception %s'%i)
continue
finally:
print('do finally %s'%i)
test5()
輸出
do stuff 0
exception 0
do finally 0
do stuff 1
exception 1
do finally 1
do stuff 2
exception 2
do finally 2
do stuff 3
exception 3
do finally 3
do stuff 4
exception 4
do finally 4
test5得到的結(jié)論:
在一個循環(huán)中,最終要跳出循環(huán)之前,會先轉(zhuǎn)到finally執(zhí)行,執(zhí)行完畢之后才開始下一輪循環(huán)
總結(jié)
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