Make variables defined in `try` visible from `else`

[jariji]

In a try/else I usually want to refer to a variable defined in the try but it's not available unless I put local x before the try.

julia> try
         x = 1
       catch 
         nothing
       else
         println(x)
       end
ERROR: UndefVarError: x not defined
Stacktrace:
 [1] top-level scope
   @ REPL[1]:5

[petvana]

I'd like to mention that try/catch/else seems undocumented now in Julia. The implementation comes from #42211. Cc: @simeonschaub

[petvana]

Btw, Python's docs provides an explicit example of a new local variable f

for arg in sys.argv[1:]:
    try:
        f = open(arg, 'r')
    except OSError:
        print('cannot open', arg)
    else:
        print(arg, 'has', len(f.readlines()), 'lines')
        f.close()

[jariji]

In Python the variable escapes all the way, which we might not want.

In [2]: try:
   ...:     x = 1
   ...: except:
   ...:     pass
   ...: 

In [3]: x
Out[3]: 1

[IanButterworth]

@simeonschaub bump on this, and the documentation.

I tried to come up with a definitive example for the docs to PR but couldn't decide on a brief one.

[simeonschaub]

try, catch and finally have always introduced new scope blocks, so this is too late to change now without causing silently wrong results in existing code. Declaring x local to the surrounding scope is the correct way to achieve this.

I will try to come up with some docs for this