Bcfg2 maintains compatibility with a wide range of Python versions – currently 2.4 through 3.2 This requires some (often significant) compatibility interfaces. This page documents the compatibility library, Bcfg2.Compat, and its contents.
Note that, due to limitations in Sphinx (the Bcfg2 documentation tool), this documentation is not automatically generated. Compat.py should always be considered the authoritative source.
There are several basic types of symbols found in Bcfg2.Compat:
To use the compatibility libraries, simply import them as such:
from Bcfg2.Compat import StringIO, all
The individual symbol import is preferred over just importing Bcfg2.Compat as a whole, since in the future we will be able to remove some items from the library and this makes that process easier. A wildcard import is definitely discouraged.
Bcfg2.Compat defines the following symbols:
The following symbols are imported to provide compatibility with Python 3. In cases where the newer symbols has also been backported to Python 2, the older symbol will be used unless otherwise noted. This is to ensure that functions or modules with radically different behavior (e.g., input()) do not cause unexpected side-effects.
The following symbols are imported or defined to provide compatibility with Python 2.4 (and occasionally 2.5). Be sure to read the notes below, since some of these implementations may be feature-incomplete.
| Name | Python 2.4 | Python 2.5+ |
|---|---|---|
| formatdate | email.Utils.formatdate() | email.utils.formatdate() |
| walk_packages | Not implemented | pkgutil.walk_packages() (2.6+) |
| any | Not implemented | any() |
| all | Not implemented | all() |
| wraps | Not implemented | functools.wraps() |
| md5 | md5.md5() | hashlib.md5 |
| MutableMapping | UserDict.DictMixin | collections.MutableMapping (2.6+) |
| literal_eval | eval() | ast.literal_eval() (2.6+) |
The walk_packages implementation for Python 2.5 is feature-complete. The implementation for Python 2.4 is not. Differences:
The wraps implementation for Python 2.4 is a no-op. It does not attempt to copy the docstring or other details from the original function to the wrapped function.
hashlib is available for Python 2.4, but it is not part of the standard base. If it is installed, it will be used. If you are doing something fancy with MD5 sums, you may need to determine which object is in use, since they are not equivalent. For the majority of simple cases – finding the MD5 sum of a string – they are equivalent enough.
collections.MutableMapping provides a subset of the functionality of UserDict.DictMixin; that is, any object that is written to work with MutableMapping will also work with DictMixin, so you should write classes with MutableMapping in mind.
collections.MutableMapping is available in Python 2.6+, and will be used if available.
ast.literal_eval() is a safe version of eval() that will only allow delaration of literal strings, ints, list, dicts, etc. This was introduced in Python 2.6, and as such Python 2.4 uses the plain-old eval().
The following functions, classes, and symbols are provided for other miscellaneous reasons.
In Python 2, base64.b64encode() and base64.b64decode() expect strings and return strings. In Python 3, they expect bytes and return bytes. For Python 3, Bcfg2.Compat provides b64encode and b64encode that transparently encode strings into bytes, then decode bytes into strings, so that those functions can be used identically to their use in Python 2.
Bases: object
In Py3K, object.__cmp__() is no longer magical, so this mixin can be used to define the rich comparison operators from __cmp__ – i.e., it makes __cmp__ magical again.
In Py3k, the unicode() class is not defined, because all strings are unicode. Bcfg2.Compat defines unicode as equivalent to str() in Python 3.
Convert a decimal number describing a POSIX permissions mode to a string giving the octal mode. In Python 2, this is a synonym for oct(), but in Python 3 the octal format has changed to 0o000, which cannot be used as an octal permissions mode, so we need to strip the ‘o’ from the output. I.e., this function acts like the Python 2 oct() regardless of what version of Python is in use.
| Parameters: | mode (int) – The decimal mode to convert to octal |
|---|---|
| Returns: | string |