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A collection of routines to help identify and morph objects.

Project description

Morph provides the following functions to help identify object types:

Name Functionality
morph.isstr(obj) Is obj a string?
morph.isseq(obj) Is obj a sequence-like (i.e. iterable) type (but not a string or dict)?
morph.isdict(obj) Is obj a dict-like type? This means that it must have at least the following methods: keys(), values(), and items().

Morph provides the following functions to help morph objects:

Name Functionality
morph.tobool(obj) Converts obj to a bool; if string-like, it is matched against a list of “truthy” or “falsy” strings; if bool-like, returns itself; then, if the default parameter is not ValueError (which defaults to False), returns that; otherwise throws a ValueError exception.
morph.tolist(obj) Converts obj to a list; if string-like, it splits it according to Unix shell semantics (if keyword split is truthy, the default); if sequence-like, returns itself converted to a list (optionally flattened if keyword flat is truthy, the default), and otherwise returns a list with itself as single object.
morph.pick(...) Extracts a subset of key/value pairs from a dict-like object where the key is a specific value or has a specific prefix.
morph.omit(...) Converse of morph.pick().
morph.flatten(obj) Converts a multi-dimensional list or dict type to a one-dimensional list or dict.
morph.unflatten(obj) Reverses the effects of flatten (note that lists cannot be unflattened).
morph.xform(obj, func) Recursively transforms sequences & dicts in object.

Flattening

When flattening a sequence-like object (i.e. list or tuple), morph.flatten recursively reduces multi-dimensional arrays to a single dimension, but only for elements of each descended list that are list-like. For example:

[1, [2, [3, 'abc', 'def', {'foo': ['zig', ['zag', 'zog']]}], 4]]

# is morphed to

[1, 2, 3, 'abc', 'def', {'foo': ['zig', ['zag', 'zog']]}, 4]

When flattening a dict-like object, it collapses list- and dict- subkeys into indexed and dotted top-level keys. For example:

{
  'a': {
    'b': 1,
    'c': [
      2,
      {
        'd': 3,
        'e': 4,
      }
    ]
  }
}

# is morphed to

{
  'a.b':      1,
  'a.c[0]':   2,
  'a.c[1].d': 3,
  'a.c[1].e': 4,
}

(This is primarily useful when dealing with INI files, which can only be flat: the flatten and unflatten functions allow converting between complex structures and flat INI files).

Note that lists can never be unflattened, and unflattening dicts is not garanteed to be round-trip consistent. The latter can happen if the dict-to-be-flattened had keys with special characters in them, such as a period ('.') or square brackets ('[]').

Picking and Omitting

Morph’s pick and omit functions allow you to extract a set of keys (or properties) from a dict-like object (or plain object). These functions will aggressively return a valid dict, regardless of the supplied value – i.e. if None is given as a source, an empty dict is returned. Furthermore, the following optional keyword parameters are accepted:

  • dict:

    Specifies the class type that should be returned, which defaults to the standard python dict type.

  • prefix:

    For pick, specifies that only keys that start with the specified string will be returned (and also filtered for the specified keys), with the prefix stripped from the keys. If no keys are specified, this will simply return only the keys with the specified prefix.

    For omit, specifies that keys that start with the specified value should be stripped from the returned dict.

  • tree:

    If specified and truthy, then the keys specified to either pick or omit are evaluated as a multi-dimensional item addresses like those produced by morph.flatten.

Examples:

d = {'foo': 'bar', 'zig.a': 'b', 'zig.c': 'd'}

morph.pick(d, 'foo', 'zig.a')
# ==> {'foo', 'bar', 'zig.a': 'b'}

morph.pick(d, prefix='zig.')
# ==> {'a': 'b', 'c': 'd'}

morph.pick(d, 'c', prefix='zig.')
# ==> {'c': 'd'}

morph.omit(d, 'foo')
# ==> {'zig.a': 'b', 'zig.c': 'd'}

morph.omit(d, prefix='zig.')
# ==> {'foo': 'bar'}

class mydict(dict): pass
morph.pick(dict(foo='bar', zig='zag'), 'foo', dict=mydict)
# ==> mydict({'foo': 'bar'})

With some limitations, this also works on object properties. For example:

class X():
  def __init__(self):
    self.foo = 'bar'
    self.zig1 = 'zog'
    self.zig2 = 'zug'
  def zigMethod(self):
    pass
x = X()

morph.pick(x, 'foo', 'zig1')
# ==> {'foo': 'bar', 'zig1': 'zog'}

morph.pick(x, prefix='zig')
# ==> {'1': 'zog', '2': 'zug'}

morph.pick(x)
# ==> {}

morph.omit(x, 'foo')
# ==> {'zig1': 'zog', 'zig2': 'zug'}

morph.omit(x, prefix='zig')
# ==> {'foo': 'bar'}

morph.omit(x)
# ==> {'foo': 'bar', 'zig1': 'zog', 'zig2': 'zug'}

Transformation

The morph.xform helper function can be used to recursively transform all the items in a list & dictionary tree – this effectively allows the ease of list comprehensions to be applied to nested list/dict structures.

Example:

morph.xform([2, [4, {6: 8}]], lambda val, **kws: val ** 2)
# ==> [4, [16, {36: 64}]]

Note that the callback function xformer, passed as the second argument to morph.xform, should always support an arbitrary number of keyword parameters (i.e. should always end the parameter list with something like **kws).

Project details


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