Python Syntax Errors with Python Anywhere

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When pasting into interactive interpreter, you must have an empty line after a block statement, before the next statement. Here’s the output from the Python Anywhere interpreter embedded on http://www.python.org:

Python 3.6.0 (default, Jan 13 2017, 00:00:00) 
[GCC 4.8.4] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> n = 5
>>> while n > 0:
...    print (n)
...    n = n - 1
... print ('Blastoff!')
  File "<stdin>", line 4
    print ('Blastoff!')
        ^
SyntaxError: invalid syntax
>>>

Writing anything in the first column to ... will cause this SyntaxError, even though legal in a source file. This is because all compound statements are passed into exec(compile(... 'single')) when completed; and the python REPL is being a bit stupid here, thinking that it was just one statement, when it is in fact while followed by a print.

Hitting enter so that the prompt returns to >>> before print will fix the problem in interactive interpreters:

Python 3.6.0 (default, Jan 13 2017, 00:00:00) 
[GCC 4.8.4] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> n = 5
>>> while n > 0:
...    print (n)
...    n = n - 1
... 
5
4
3
2
1
>>> print ('Blastoff!')
Blastoff!
>>>

But notice that the while loop now runs as soon as the compound statement is terminated, i.e. before the >>> prompt shows again.

There are other shells besides the standard Python REPL. One popular, ipython, has a console shell that will recognize copy-pasted content and run this one correctly:

% ipython
Python 3.5.3 (default, Jan 19 2017, 14:11:04) 
Type 'copyright', 'credits' or 'license' for more information
IPython 6.1.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: n = 5
   ...: while n > 0:
   ...:    print (n)
   ...:    n = n - 1
   ...: print ('Blastoff!')
   ...: 
5
4
3
2
1
Blastoff!

In [2]:

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