What's the difference between running a script under command box and interpreter?

[Cameron Simpson]

On 31Oct2019 22:03, Jach Fong <jfong at ms4.hinet.net> wrote:
>Cameron Simpson於 2019年11月1日星期五 UTC+8下午12時13分45秒寫道：
>> On 31Oct2019 20:44, Jach Fong <jfong at ms4.hinet.net> wrote:
>> >The script test.py is something like this:
>> >-------test.py
>> >from pyeds import fsm
>> >...
>> >class Rule_Parse:
>> >    def __init__(self):
>> >        ...
>> >        self.current_char = ''
>> >...
>> >def main(input_str):
>> >    for c in input_str:
>> >        ...
>> >        rule.current_char = c
>> >        ...
>> >
>> >if __name__ == '__main__':
>> >    input_str = '(NNS(acoustics) & RB(not)) | JJ(muted)'
>> >    rule = Rule_Parse()
>> >    main(input_str)
>> >    ...
>> >
>> >-----------
>> >The test.py can run correctly under command box:
>> >D:\Works\Python\pyeds-master\src>py test.py
>> >
>> >but fails when running under interpreter:
>> >D:\Works\Python\pyeds-master\src>py
>> >Python 3.4.4 (v3.4.4:737efcadf5a6, Dec 20 2015, 19:28:18) [MSC v.1600 32 bit (Intel)] on win32
>> >Type "help", "copyright", "credits" or "license" for more information.
>> >>>> from test import *
>> >>>> input_str = "(NNS(acoustics) & RB(not)) | JJ(muted)"
>> >>>> rule = Rule_Parse()
>> >>>> main(input_str)
>> >Traceback (most recent call last):
>> >  File "<stdin>", line 1, in <module>
>> >  File "D:\Works\Python\pyeds-master\src\test.py", line 229, in main
>> >    rule.current_char = c
>> >NameError: name 'rule' is not defined
>> >>>>
>> >
>> >I did check the globals using dir() and the 'rule' is there, no doubt.
>>
>> It matters how you checked this. This isn't apparent.
[...]
>Yes, the 'if' body is not executed when I import test.py under 
>interpreter, that's why I manually execute them there.
>What puzzles me is that the globals() has a 'rule' object in both 
>cases. Why this one doesn't work?

I think I have misinterpreted what you've done.

The globals are your current module's namespace, and functions defines 
in a module are bound to that module's namespace.

Strip your test.py back. A lot. Try this:

    def main():
      print(rule)

Now, let's use that:

    Python 3.7.4 (default, Sep 28 2019, 13:34:38)
    [Clang 8.0.0 (clang-800.0.42.1)] on darwin
    Type "help", "copyright", "credits" or "license" for more information.
    >>> import test
    >>> test.main()
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "/Users/cameron/tmp/d1/test.py", line 2, in main
        print(rule)
    NameError: name 'rule' is not defined

What's happening here?

When we call main it tries to print "rule" from its module's globals.  

The first time you call it that doesn't exist, and we get your error.

Setting rule=1 in the interpreter's space doesn't help (the stuff below 
if from the same session continued from above):

    >>> rule=1
    >>> test.main()
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "/Users/cameron/tmp/d1/test.py", line 2, in main
        print(rule)
    NameError: name 'rule' is not defined

But if we define rule in the "test" module things improve:

    >>> test.rule=2
    >>> test.main()
    2

Importing main from test doesn't change where it looks for its globals:

    >>> from test import main as my_main
    >>> my_main()
    2

That value (2) is still coming out of the test module.

Cheers,
Cameron Simpson <cs at cskk.id.au>