New submission from Leo:
The nametuple function creates classes dynamically. The caller must provide the
class name thus overriding any existing object name.
An overridden object may be garbage-collected
or survive depending on its reference count.
While this behavior is not new to Python, I am unaware of a simple function
with such an awkward side effect.
One might consider this a feature rather than a bug
thus shifting responsibility for carefully passing suitable class names to
nametuple.
However, I believe nametuple should raise an exception
if the provided name would override an existing name. If needed, this behavior
could be made
customizable by a keyword argument override defaulting to False.
Consequently, the caller would have to delete the object under that
name explicitly before calling nametuple. This behavior would increase code
clarity and eliminate´ a source of subtle
errors.
The code example given below shows the survival of
a pre-existing class due to an instance linked to it. As a consequence, two
different classes with the same name exist. Only the posterior is,
however, bound to the
__main__ namespace. The prior is no longer known to that namespace potentially
breaking
remote parts of the code.
In [1]: from collections import namedtuple
In [2]: AB=namedtuple('AB', ('a','b'))
In [3]: ab=AB(4,9)
In [4]: type(ab)
Out[4]: __main__.AB
In [6]: AB=namedtuple('AB', ('c','d'))
In [7]: type(ab)
Out[7]: __main__.AB
In [8]: ab2=AB(16,25)
In [9]: type(ab2)
Out[9]: __main__.AB
In [10]: type(ab)
Out[10]: __main__.AB
In [11]: ab
Out[11]: AB(a=4, b=9)
In [12]: ab2
Out[12]: AB(c=16, d=25)
----------
components: Library (Lib)
messages: 228641
nosy: fhaxbo...@googlemail.com
priority: normal
severity: normal
status: open
title: namedtuple: raise an exception when the given class name would override
an existing name
type: behavior
versions: Python 3.4
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue22563>
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