[New-bugs-announce] [issue6924] struct.unpack weird behavior with "bi" (byte then integer)

[Emmanuel Bengio]

New submission from Emmanuel Bengio <bengioe at gmail.com>:

Using the following command in Python 2.6.1:

>>> struct.unpack("BI","12345")
Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    struct.unpack("BI","12345")
error: unpack requires a string argument of length 8

I get this error message. What confused me was that doing
>>> struct.unpack("IB","12345")
(875770417, 53)
Worked just fine.

I have found out that this only happens using the native byte
order("@"), which is the default.
For Example:
>>> struct.unpack("!BI","12345")
(49, 842216501)
Works, and all other variants, =, <, > (native standard,little endian,
and small endian) also do.

I haven't found anything about that in the documentation.

Also, the requested 3 other bytes arent event used:
>>> struct.unpack("I","abcd")
(1684234849,) # see the big number starting with 16
>>> ord("x")
120
>>> struct.unpack("BI","xabcd") # we get the error
Traceback (most recent call last):
  File "<pyshell#7>", line 1, in <module>
    struct.unpack("BI","xabcd")
error: unpack requires a string argument of length 8
>>> struct.unpack("BI","xabcdefg")
(120, 1734763876) # not the same here
>>> struct.unpack("BI","xabcabcd")
(120, 1684234849) # same here
>>> struct.unpack("BI","x___abcd")
(120, 1684234849) # same again

----------
components: Library (Lib)
messages: 92724
nosy: Manux
severity: normal
status: open
title: struct.unpack weird behavior with "bi" (byte then integer)
type: behavior
versions: Python 2.6

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue6924>
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