try, except, else and finally

Syntax

try:
    if there is error, go to except
    Else, go to else
except:
    Something
else:
    Something
finally:
    always execute this one at the end
    OR execute on the way of return/out

The finally clause is always executed on the way out. If there isn’t explict return, finally will execute at the very end. The return value is determined by the first return statement executed. If return in try or else, since the finally clause always being executed on the way out, it will jump to finally clause (finally clause hijack return process). If finally clause has return statement, this statement will be excuated and as return value.

Example: without explict return

def foo():
    try:
        a = 1/1
    except:
        print('except')
    else:
        print('else')
    finally:
        print('final')

>>> foo()
else
final

Example: return in else

def foo():
    try:
        a = 1/1
    except:
        print('except')
    else:
        print('else')
        return 1
    finally:
        print('final')

>>> foo()
else
final
Out[1]: 1

Example: return in else and finally

def foo():
    try:
        a = 1/1
    except:
        print('except')
    else:
        print('else')
        return 1
    finally:
        print('final')
        return 0

>>> foo()
else
final
Out[1]: 0