REPL with multiple function definitions

Rob Cliffe

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Jun 26, 2022, 6:14:57 PM6/26/22

to

This 2-line program

def f(): pass
def g(): pass

runs silently (no Exception). But:

23:07:02 c:\>python
Python 3.8.3 (tags/v3.8.3:6f8c832, May 13 2020, 22:20:19) [MSC v.1925 32
bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> def f(): pass
... def g(): pass
File "<stdin>", line 2
def g(): pass
^
SyntaxError: invalid syntax
>>>

Is there a good reason for this?
Thanks
Rob Cliffe

Jon Ribbens

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Jun 26, 2022, 6:22:50 PM6/26/22

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For some reason, the REPL can't cope with one-line blocks like that.
If you put a blank line after each one-block line then it will work.

Chris Angelico

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Jun 26, 2022, 6:37:31 PM6/26/22

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On Mon, 27 Jun 2022 at 08:15, Rob Cliffe via Python-list
<pytho...@python.org> wrote:
>
> This 2-line program
>
> def f(): pass
> def g(): pass
>
> runs silently (no Exception). But:
>
> 23:07:02 c:\>python
> Python 3.8.3 (tags/v3.8.3:6f8c832, May 13 2020, 22:20:19) [MSC v.1925 32
> bit (Intel)] on win32
> Type "help", "copyright", "credits" or "license" for more information.
> >>> def f(): pass
> ... def g(): pass
> File "<stdin>", line 2
> def g(): pass
> ^
> SyntaxError: invalid syntax
> >>>
>
> Is there a good reason for this?

The REPL compiles one statement at a time. A file is allowed to
contain multiple statements.

ChrisA

Roel Schroeven

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Jun 26, 2022, 6:38:18 PM6/26/22

to

Rob Cliffe via Python-list schreef op 27/06/2022 om 0:14:

> This 2-line program
>
> def f(): pass
> def g(): pass
>
> runs silently (no Exception). But:
>
> 23:07:02 c:\>python
> Python 3.8.3 (tags/v3.8.3:6f8c832, May 13 2020, 22:20:19) [MSC v.1925 32
> bit (Intel)] on win32
> Type "help", "copyright", "credits" or "license" for more information.
> >>> def f(): pass
> ... def g(): pass
> File "<stdin>", line 2
> def g(): pass
> ^
> SyntaxError: invalid syntax
> >>>
>
> Is there a good reason for this?

The REPL requires an extra empty line to indicate the end of multi-line
constructs. You can see it by the prompt: as long as the REPL prints
'... ' as prompt, that means it puts everything you type in the same
multi-line construct. To enter a new multi-line construct (such as a
function definition, a for-loop, an if-statement, ...), press enter
directly at the prompt; the REPL should than use '>>> ' as the prompt again.

(Alternatives like IPython (https://ipython.readthedocs.io/en/stable/)
are a bit more loose regarding how to enter multi-line constructs)

--
"Iceland is the place you go to remind yourself that planet Earth is a
machine... and that all organic life that has ever existed amounts to a greasy
film that has survived on the exterior of that machine thanks to furious
improvisation."
-- Sam Hughes, Ra

Rob Cliffe

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Jun 28, 2022, 8:59:09 PM6/28/22

to

It's actually not to do with 1-line blocks, just attempting to define 2
functions "at once":

22:27:23 C:\>python

Python 3.8.3 (tags/v3.8.3:6f8c832, May 13 2020, 22:20:19) [MSC v.1925 32
bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> def f():

...     return 42
... def g():
File "<stdin>", line 3
    def g():
    ^
SyntaxError: invalid syntax
>>>

But you are right that adding a blank line after the first function
definition solves the "problem".
Rob Cliffe

Chris Angelico

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Jun 28, 2022, 9:14:03 PM6/28/22

to

On Wed, 29 Jun 2022 at 11:00, Rob Cliffe via Python-list
<pytho...@python.org> wrote:
>
> On 26/06/2022 23:22, Jon Ribbens via Python-list wrote:

> It's actually not to do with 1-line blocks, just attempting to define 2
> functions "at once":
>
>

> 22:27:23 C:\>python

> Python 3.8.3 (tags/v3.8.3:6f8c832, May 13 2020, 22:20:19) [MSC v.1925 32
> bit (Intel)] on win32
> Type "help", "copyright", "credits" or "license" for more information.
> >>> def f():

> ... return 42
> ... def g():
> File "<stdin>", line 3
> def g():
> ^
> SyntaxError: invalid syntax
> >>>
>
> But you are right that adding a blank line after the first function
> definition solves the "problem".

And if you have something where you want to copy and paste multiple
statements, there are a few ways to do it:

1) Put "if 1:" at the top. That makes it a single block, so you can
paste in as much as you like, as long as the only blank line is at the
end.

2) Put the code into a file and then use "python3 -i setup.py". That
runs all the code, then drops you into the REPL in that context.

3) Put the code into a file, and inside the REPL, "from setup import
*". Unlike option 2, this can be done after the beginning of the
session. Downside: editing setup.py and reimporting won't apply your
changes.

ChrisA