[New-bugs-announce] [issue39495] xml.etree.ElementTree.TreeBuilder.start differs between pure Python and C implementations

[Shantanu]

New submission from Shantanu <hauntsaninja at gmail.com>:

The C accelerated version of `xml.etree.ElementTree.TreeBuilder.start` has a default value for `attrs`, whereas the pure Python version does not.

```
In [41]: sys.version                                                                                                               
Out[41]: '3.8.1 (default, Jan 23 2020, 23:36:06) \n[Clang 11.0.0 (clang-1100.0.33.17)]'

In [42]: import xml.etree.ElementTree                                                                                              

In [43]: inspect.signature(xml.etree.ElementTree.TreeBuilder.start)                                                                
Out[43]: <Signature (self, tag, attrs=None, /)>

In [44]: from test.support import import_fresh_module                                                                              

In [45]: pyElementTree = import_fresh_module('xml.etree.ElementTree', blocked=['_elementtree'])                                    

In [46]: inspect.signature(pyElementTree.TreeBuilder.start)                                                                        
Out[46]: <Signature (self, tag, attrs)>
```

>From PEP 399 (https://www.python.org/dev/peps/pep-0399/)
```
Acting as a drop-in replacement also dictates that no public API be provided in accelerated code that does not exist in the pure Python code. Without this requirement people could accidentally come to rely on a detail in the accelerated code which is not made available to other VMs that use the pure Python implementation. 
```

----------
components: Library (Lib)
messages: 361002
nosy: hauntsaninja
priority: normal
severity: normal
status: open
title: xml.etree.ElementTree.TreeBuilder.start differs between pure Python and C implementations

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue39495>
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