Why does this code give me a syntax error in idle?
if I use python online, which was correct.
I was expecting an output like the second photo. What is the problem and how can I fix it?
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1Don't post images of code, errors or data. Post the text in the question. See How to AskTangentially Perpendicular– Tangentially Perpendicular2023-11-29 19:56:16 +00:00Commented Nov 29, 2023 at 19:56
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@TangentiallyPerpendicular - In this particular case images are necessary to demonstrate the difference between two environments.PM 77-1– PM 77-12023-11-29 20:01:06 +00:00Commented Nov 29, 2023 at 20:01
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@PM77-1 No image is needed. See my answer with proper quoted text as T.P. requested.Terry Jan Reedy– Terry Jan Reedy2023-12-01 16:48:43 +00:00Commented Dec 1, 2023 at 16:48
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1 Answer
This issue is NOT about IDLE. Rather, it is about interactive mode versus batch (file) mode. In an interactive REPR (Read-Execute_PRint*) loop, the interpreter reads, executes, and prints the result of one command/statement/expression at a time. Submitting more than one at a time is usually an error. In batch mode, the interpreter reads multiple execution units at once.
In Python, execution units can span more than one physical line. Here is Python's standard REPL mode.
>>> def f():
... print(1)
... f()
File "<stdin>", line 3
f()
^
SyntaxError: invalid syntax
In Python, the end of a compound statememt (one with a header terminated by :) is signaled by a blank line. See this tutorial section. Adding a blank line to the above results in:
>>> def f():
... print(1)
...
>>> f()
1
The online python used has a batch mode editor (and submit file mechanism) and therefore did not have the interactive mode start '>>>' and continuation '...' prompts. Thus, no blank line is required.
* I am aware that the 'E' is usually taken to mean 'Eval' (from 'evaluate an expression', as in Lisp) rather that 'Execute', but the latter is more appropriate for statements.