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79 lines
2.6 KiB
Python
79 lines
2.6 KiB
Python
'''
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This module sets up a scheme for validating that arbitrary Python
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objects are correctly typed. It is totally decoupled from Django,
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composable, easily wrapped, and easily extended.
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A validator takes two parameters--var_name and val--and returns an
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error if val is not the correct type. The var_name parameter is used
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to format error messages. Validators return None when there are no errors.
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Example primitive validators are check_string, check_int, and check_bool.
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Compound validators are created by check_list and check_dict. Note that
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those functions aren't directly called for validation; instead, those
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functions are called to return other functions that adhere to the validator
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contract. This is similar to how Python decorators are often parameterized.
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The contract for check_list and check_dict is that they get passed in other
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validators to apply to their items. This allows you to build up validators
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for arbitrarily complex validators. See ValidatorTestCase for example usage.
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A simple example of composition is this:
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check_list(check_string)('my_list', ['a', 'b', 'c']) == None
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To extend this concept, it's simply a matter of writing your own validator
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for any particular type of object.
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'''
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def check_string(var_name, val):
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if not isinstance(val, basestring):
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return '%s is not a string' % (var_name,)
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return None
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def check_int(var_name, val):
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if not isinstance(val, int):
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return '%s is not an integer' % (var_name,)
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return None
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def check_bool(var_name, val):
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if not isinstance(val, bool):
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return '%s is not a boolean' % (var_name,)
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return None
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def check_list(sub_validator, length=None):
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def f(var_name, val):
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if not isinstance(val, list):
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return '%s is not a list' % (var_name,)
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if length is not None and length != len(val):
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return '%s should have exactly %d items' % (var_name, length)
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for i, item in enumerate(val):
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vname = '%s[%d]' % (var_name, i)
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error = sub_validator(vname, item)
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if error:
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return error
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return None
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return f
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def check_dict(required_keys):
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# required_keys is a list of tuples of
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# key_name/validator
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def f(var_name, val):
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if not isinstance(val, dict):
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return '%s is not a dict' % (var_name,)
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for k, sub_validator in required_keys:
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if k not in val:
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return '%s key is missing from %s' % (k, var_name)
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vname = '%s["%s"]' % (var_name, k)
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error = sub_validator(vname, val[k])
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if error:
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return error
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return None
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return f
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