New submission from Steven Barker:
Pasting multiple lines of input and then pressing Enter when IDLE is waiting to
read a single line (such as when input() or sys.stdin.readline() have been
called) will result is a multi-line string being given as the input, rather
than a single line.
This may be most easily understood by looking at an example. Run this code in
IDLE (either by typing it in the shell, or from a file with F5):
s = "X"
while s:
s = input()
print(repr(s))
First, try typing in several lines. Each will be printed separately, with no
newlines inside the strings (since input() strips a trailing newline).
foo
'foo'
bar
'bar'
baz
'baz'
Next, copy several lines of text from somewhere. It doesn't matter what the
lines' contents are. Here I grabbed a list of Python version numbers, as I was
on the download page after grabbing 3.4.0b1 for testing this bug:
3.1.5
3.0.1
2.7.6
2.6.9
2.5.6
2.4.6
2.3.7
2.2.3 <all the preceding lines were pasted in one go, followed by enter
pressed here>
'3.1.5\n3.0.1\n2.7.6\n2.6.9\n2.5.6\n2.4.6\n2.3.7\n2.2.3'
This behavior is different than what the Python interpreter does in a regular
console shell. When running in cmd.exe on Windows, Python treats a multi-line
paste just like typed input:
3.1.5
'3.1.5'
3.0.1
'3.0.1'
2.7.6
'2.7.6'
2.6.9
'2.6.9'
2.5.6
'2.5.6'
2.4.6
'2.4.6'
2.3.7
'2.3.7'
2.2.3 <enter typed here>
'2.2.3'
I expect the same behavior will be common in other kinds of terminals on other
platforms.
This issue makes testing certain kinds of programs very frustrating. If your
program needs to read certain text from STDIN, and you want to paste that text
in quickly, you need to update your code with special logic just for use in
IDLE's console. As an example of the kind of pain you may experience, try
copying and pasting a block of text with a blank line into the input loop
above. On a regular console session it will exit the loop after the blank line.
In IDLE, it will keep running.
I've traced the source of this issue through IDLE's sys.stdin file object and
an RPC call, and found it probably is located in the
idlelib.PyShell.PyShell.readline method (or the surrounding code). This grabs a
string from the Text object in the shell window and returns it to the Python
code running in the subprocess.
Probably it should have some extra steps added to check if it got multiple
lines. If so, it should split the string on newlines and return just one line
of text for each readline call. I'm not sure exactly what should be done with
the rest of the lines, but perhaps they could be queued up (or somehow "put
back" by moving the markers in the Text object) so later lines would be grabbed
by later input requests.
Or alternatively, maybe the event where the multi-line paste arrives should be
handled differently, as several single-line input events, rather than a single
multiple-line one.
----------
components: IDLE
messages: 206879
nosy: Steven.Barker
priority: normal
severity: normal
status: open
title: IDLE's shell returns a multiple-line string to input() or readline()
when multiple lines of text are pasted by the user
type: behavior
versions: Python 2.7, Python 3.3, Python 3.4
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Python tracker <[email protected]>
<http://bugs.python.org/issue20058>
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