Multiple try codes in one block

Question

I have a problem with my code in the try block. To make it easy this is my code:

try:
    code a
    code b #if b fails, it should ignore, and go to c.
    c         


        

Answer 1

If you don't want to chain (a huge number of) try-except clauses, you may try your codes in a loop and break upon 1st success.

Example with codes which can be put into functions:

for code in (
    lambda: a / b,
    lambda: a / (b + 1),
    lambda: a / (b + 2),
    ):
    try: print(code())
    except Exception as ev: continue
    break
else:
    print("it failed: %s" % ev)

Example with arbitrary codes (statements) directly in the current scope:

for i in 2, 1, 0:
    try:
        if   i == 2: print(a / b)
        elif i == 1: print(a / (b + 1))
        elif i == 0: print(a / (b + 2))
        break        
    except Exception as ev:
        if i:
            continue
        print("it failed: %s" % ev)

Answer 2

Lets say each code is a function and its already written then the following can be used to iter through your coding list and exit the for-loop when a function is executed without error using the "break".

def a(): code a
def b(): code b
def c(): code c
def d(): code d

for func in [a, b, c, d]:  # change list order to change execution order.
   try:
       func()
       break
   except Exception as err:
       print (err)
       continue

I used "Exception " here so you can see any error printed. Turn-off the print if you know what to expect and you're not caring (e.g. in case the code returns two or three list items (i,j = msg.split('.')).

Answer 3

You can use fuckit module.
Wrap your code in a function with @fuckit decorator:

@fuckit
def func():
    code a
    code b #if b fails, it should ignore, and go to c.
    code c #if c fails, go to d
    code d

Answer 4

You could try a for loop

for func,args,kwargs in zip([a,b,c,d], 
                            [args_a,args_b,args_c,args_d],
                            [kw_a,kw_b,kw_c,kw_d]):
    try:
       func(*args, **kwargs)
       break
    except:
       pass

This way you can loop as many functions as you want without making the code look ugly

Answer 5

You'll have to make this separate try blocks:

try:
    code a
except ExplicitException:
    pass

try:
    code b
except ExplicitException:
    try:
        code c
    except ExplicitException:
        try:
            code d
        except ExplicitException:
            pass

This assumes you want to run code c only if code b failed.

If you need to run code c regardless, you need to put the try blocks one after the other:

try:
    code a
except ExplicitException:
    pass

try:
    code b
except ExplicitException:
    pass

try:
    code c
except ExplicitException:
    pass

try:
    code d
except ExplicitException:
    pass

I'm using except ExplicitException here because it is never a good practice to blindly ignore all exceptions. You'll be ignoring MemoryError, KeyboardInterrupt and SystemExit as well otherwise, which you normally do not want to ignore or intercept without some kind of re-raise or conscious reason for handling those.

Answer 6

Extract (refactor) your statements. And use the magic of and and or to decide when to short-circuit.

def a():
    try: # a code
    except: pass # or raise
    else: return True

def b():
    try: # b code
    except: pass # or raise
    else: return True

def c():
    try: # c code
    except: pass # or raise
    else: return True

def d():
    try: # d code
    except: pass # or raise
    else: return True

def main():   
    try:
        a() and b() or c() or d()
    except:
        pass