Add PEP 221: "Import As", as posted on python-dev.

pep-0221.txt

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+PEP: 221
+Title: Import As
+Version: $Revision$
+Owner: thomas@xs4all.net (Thomas Wouters)
+Python-Version: 2.0
+Status: Draft
+Created: 15-Aug-2000
+Type: Standard
+
+
+Introduction
+
+    This PEP describes the `import as' proposal for Python 2.0. This
+    PEP tracks the status and ownership of this feature. It contains a
+    description of the feature and outlines changes necessary to
+    support the feature. The CVS revision history of this file
+    contains the definitive historical record.
+
+
+Rationale
+
+    This PEP proposes a small extention of current Python syntax
+    regarding the `import' and `from <module> import' statements. 
+    These statements load in a module, and either bind that module to
+    a local name, or binds objects from that module to a local name. 
+    However, it is sometimes desirable to bind those objects to a
+    different name, for instance to avoid name clashes. Currently, a
+    round-about way has to be used to achieve this:
+
+    import os
+    real_os = os
+    del os
+    
+    And similar for the `from ... import' statement:
+    
+    from os import fdopen, exit, stat
+    os_fdopen = fdopen
+    os_stat = stat
+    del fdopen, stat
+    
+    The proposed syntax change would add an optional `as' clause to
+    both these statements, as follows:
+
+    import os as real_os
+    from os import fdopen as os_fdopen, exit, stat as os_stat
+    
+    The `as' name is not intended to be a keyword, and some trickery
+    has to be used to convince the CPython parser it isn't one. For
+    more advanced parsers/tokenizers, however, this should not be a
+    problem.
+
+
+Implementation details
+
+    A proposed implementation of this new clause can be found in the
+    SourceForge patch manager[XX]. The patch uses a NAME field in the
+    grammar rather than a bare string, to avoid the keyword issue. It
+    also introduces a new bytecode, IMPORT_FROM_AS, which loads an
+    object from a module and pushes it onto the stack, so it can be
+    stored by a normal STORE_NAME opcode.
+    
+    The special case of `from module import *' remains a special case,
+    in that it cannot accomodate an `as' clause. Also, the current
+    implementation does not use IMPORT_FROM_AS for the old form of
+    from-import, even though it would make sense to do so. The reason
+    for this is that the current IMPORT_FROM bytecode loads objects
+    directly from a module into the local namespace, in one bytecode
+    operation, and also handles the special case of `*'. As a result
+    of moving to the IMPORT_FROM_AS bytecode, two things would happen:
+    
+    - Two bytecode operations would have to be performed, per symbol,
+      rather than one.
+      
+    - The names imported through `from-import' would be susceptible to
+      the `global' keyword, which they currently are not. This means
+      that `from-import' outside of the `*' special case behaves more
+      like the normal `import' statement, which already follows the
+      `global' keyword. It also means, however, that the `*' special
+      case is even more special, compared to the ordinary form of
+      `from-import'
+
+    However, for consistency and for simplicity of implementation, it
+    is probably best to split off the special case entirely, making a
+    separate bytecode `IMPORT_ALL' that handles the special case of
+    `*', and handle all other forms of `from-import' the way the
+    proposed `IMPORT_FROM_AS' bytecode does.
+
+    This dilemma does not apply to the normal `import' statement,
+    because this is alread split into two opcodes, a `LOAD_MODULE' and a
+    `STORE_NAME' opcode. Supporting the `import as' syntax is a slight
+    change to the compiler only.
+
+
+Copyright
+
+    This document has been placed in the Public Domain.
+
+
+References
+
+    [1]
+http://sourceforge.net/patch/?func=detailpatch&patch_id=101135&group_id=5470
+
+
+
+Local Variables:
+mode: indented-text
+indent-tabs-mode: nil
+End: