[Tutor] Python printing parentheses and quotes

[Sai Allu]

Thank you Cameron,

This was something that I was working on last week and I've been able to fix the script since then. I was just curious why the previous version did that and you might be right, thank you for the help though!

Best Wishes,
Sai Allu
________________________________
From: Cameron Simpson <cs at cskk.id.au>
Sent: Monday, June 10, 2019 5:34 PM
To: Sai Allu
Cc: Mats Wichmann; tutor at python.org; Deepak Dixit
Subject: Re: [Tutor] Python printing parentheses and quotes

On 10Jun2019 19:04, Sai Allu <sai.allu at nutanix.com> wrote:
>Actually I'm pretty sure what happened was that the "#! usr/bin/python" was in a module that was being imported. So the Python interpreter cached it or somehow crashed randomly, which meant that the print was working as a keyword instead of a function.
>
>But when I removed that "#! usr/bin/python" line and then rewrote the print statements, it went back to working normally.

My personal suspicision is that what you might have been doing is this
(notice the trailing comma):

  print("",)

or maybe:

  print("this", that")

Look:

  % python
  Python 2.7.16 (default, Apr  1 2019, 15:01:04)
  [GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.42.1)] on darwin
  Type "help", "copyright", "credits" or "license" for more information.
  >>> print("",)
  ('',)
  >>>

  % python3
  Python 3.7.3 (default, Mar 30 2019, 03:38:02)
  [Clang 8.0.0 (clang-800.0.42.1)] on darwin
  Type "help", "copyright", "credits" or "license" for more information.
  >>> print("",)

  >>>

What is happening?

In Python 2, print is a statement unless you use the __future__ import
already mentioned. That means that this:

  print("",)

is a "print" of the expression ("",), which is a 1-tuple, and gets
printed as a tuple. The more likely scenario is when you're printing
mulitple things:

  print("this", "that")

which is still a "print" of a tuple.

However, in Python 3 print is a function which means that the brackets
are part of the function call. So this:

  print("")

or:

  print("this", "that")

is a call to the "print()" function, passing one or two arguments, which
get printed. And printing "" (the former case) is an empty string.

Please revisit your code can test this.

Subtle issues like this are why we like to receive _exact_ cut/paste of
your code and the matching output, not a retype of what you thought you
ran. If you encounter something weird like this, it is well worth your
time (and ours) if you make a tiny standalone script showing the
problem, as small as possible. Then paste it into your message and paste
in the output (this list drops attachments). That we we can all run
exactly the same code, and solve your actual problem.

And start always using:

  from __future__ import print_function

in Python if you're using print. That will make your prints behave the
same regardless if whether they are using Python 2 or 3.

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