withref Uses the with statement to simplify complex dereferences--somewhat like in Pascal or JavaScript
Download

withref Ranking & Summary

withref Tags

JavaScript Python library Python Pascal

withref Description

withref is a Python module that makes Python's with statement able to simplify complex dereferences. This is what I initially, naively thought the statement was for, similar to the with statement of half-remembered Pascal.The typical Python use is a more complex guard over the entry and exit points for using an object. See e.g. this effbot article. But withref makes this simpler "just give me the dereferenced object, please" use case work as well.Usage from withref import ref from easydict import EasyDict # EasyDict used for demonstration purposes only. Convenient way to # make dict entries accessible as dot-deferenceable properties. a = EasyDict({ 'b': { 'c': { 'c1': 1 }, 'd': 44.1 } }) with ref(a.b.c) as c: c.c1 = 99 print a a_ideal = EasyDict({'b': {'c': {'c1': 99}, 'd': 44.1}}) assert a == a_ideal It works with array-style references too, of course:: with ref(a) as cc: c = 99 assert a == a_ideal But beware OVER-dereferencing! While this works correctly:: with ref(a.b.c.c1) as c1: print c1 assert c1 == 99This does NOT:: with ref(a.b.c.c1) as c1: c1 = 12345 assert c1 == 12345 assert a.b.c.c1 == 99 # with heavy heartUnlike Pascal, ref is not built into the language proper. And unlike Perl, Python is less eager to provide lvalues for every mention of a variable or value. As a result, ``ref`` can provide the *value* of the full-deferenced ``c1``, but not the assignable *lvalue*.Like Pascal's ``with``, ``ref`` removes N-1 layers of the enclosing structure for values, but only N-2 for assignment. Still, in complex multi-layer structures, this can be a nice simplification:: with ref(app.config.server.wsgi) as wsgi: wsgi.logger = some_logger wsgi.debug_level = 4 wsgi.port = 8080 arguably beats:: app.config.server.wsgi.logger = some_logger app.config.server.wsgi.debug_level = 4 app.config.server.wsgi.port = 8080for simplicity and clarity.I see a lot of configuration code that constantly repeats the same long multi-level dereferences. That style is repetitive (anti-DRY) and tends to left-align code blocks, both of which impede program comprehension. Using the with statement is a neat way to simplify and at the same time add a little extra visual structure.And while assignment ("lvalue production") isn't always possible, there still are some interesting tricks possible with simple value production: with ref("this is a string") as t: print tAlternativeWhile yadda.yadda.yadda referencing is all too common, one can alsouse a more proximate variable assignment:: wsgi = app.config.server.wsgi wsgi.logger = some_logger wsgi.debug_level = 4 wsgi.port = 8080 This lacks the more indented structure of the withref approach, but is still much preferable to what you often find in the field.See AlsoThe withhacks module, which includes many other fun hacks (multi-line lambdas, new looping structures, etc.)--but also requires the byteplay module which actively introspects & munges Python bytecode ("Danger, Will Robinson! Danger!"), and has not been updated to work beyond Python 2.6.Possible Future ExtensionAs "withhacks" shows, using introspection we could determine the lvalue of the calling object even in the edge-case where it is a leaf-node of its enclosing structure. This would not require any bytecode changes, and should be compatible with modern versions of Python (e.g. 2.7.x and 3.x).Whether that trick can be done simply, portably, rock-solid reliably, and transparently enough to satisfy those who code the modules that tend to most need this kind of dereferencing simplification--i.e. complex modules often used in production settings, into which they are understandably loathe to introduce any possible sources of error or any performance impedance--that is the key open question.Installation pip install withref To use the test and demonstration code as shown here, also:: pip install easydict (You may need to prefix these with "sudo " to authorize installation.)Product's homepage

withref Related Software