Nothing (almost) should ever be any str or any int
Documentation: valtypes.readthedocs.io
Source code: github.com/LeeeeT/valtypes
Valtypes is a flexible data parsing library which will help you make illegal states unrepresentable and enable you to practice "Parse, don’t validate" in Python. It has many features that might interest you, so let's dive into some examples.
Create constrained types:
from valtypes.type.str import NonEmpty, MaximumLength
class Name(NonEmpty, MaximumLength):
__maximum_length__ = 20
def initials(name: Name) -> str:
# name is guaranteed to be a non-empty string of maximum length 20
return f"{name[0]}."
initials(Name("Fred")) # passes
initials(Name("")) # parsing error
initials("") # fails at static type checkingParse complex data structures:
from dataclasses import dataclass
from valtypes import parse_json
from valtypes.type import int, list, str
@dataclass
class User:
id: int.Positive
name: Name
hobbies: list.NonEmpty[str.NonEmpty]
raw = {"id": 1, "name": "Fred", "hobbies": ["origami", "curling", "programming"]}
print(parse_json(User, raw))User(id=1, name='Fred', hobbies=['origami', 'curling', 'programming'])
Get a nice error message if something went wrong (traceback omitted):
raw = {"id": 0, "hobbies": [""]}
parse_json(User, raw)| valtypes.error.parsing.dataclass.Composite: dataclass parsing error (3 sub-exceptions)
+-+---------------- 1 ----------------
| valtypes.error.parsing.dataclass.WrongFieldValue: can't parse field 'id' (1 sub-exception)
+-+---------------- 1 ----------------
| valtypes.error.parsing.type.numeric.Minimum: the value must be greater than or equal to 1, got: 0
+------------------------------------
+---------------- 2 ----------------
| valtypes.error.parsing.dataclass.MissingField: required field 'name' is missing
+---------------- 3 ----------------
| valtypes.error.parsing.dataclass.WrongFieldValue: can't parse field 'hobbies' (1 sub-exception)
+-+---------------- 1 ----------------
| valtypes.error.parsing.sequence.Composite: sequence parsing error (1 sub-exception)
+-+---------------- 1 ----------------
| valtypes.error.parsing.sequence.WrongItem: can't parse item at index 0 (1 sub-exception)
+-+---------------- 1 ----------------
| valtypes.error.parsing.type.sized.MinimumLength: length 0 is less than the allowed minimum of 1
+------------------------------------
Install from PyPI:
pip install valtypesBuild the latest version from source:
pip install git+https://github.com/LeeeeT/valtypes
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