typedpath 0.1.2

Use typed Python objects to represent files and directories.

typedpath

Use typed Python objects to represent files and directories.

If you have a project that reads or writes non-trivial structures of directories and files it can be hard to keep track of which structure they should have. typedpath allow you to declare the structure using Python objects, and access the data with object methods.

Example:

import typedpath as tp


class Person(tp.StructDir):
    name: tp.TextFile
    config: tp.JSONFile


class Database(tp.StructDir):
    people: tp.DictDir[str, Person]


d = Database("database")
d.people["alice"].name.write("Alice")
d.people["alice"].config.write({"require_authentication": True})
d.people["bob"].name.write("Bob")
d.people["bob"].config.write({"require_authentication": False})

> tree database/
database/
└── people
    ├── alice
    │   ├── config.json
    │   └── name.txt
    └── bob
        ├── config.json
        └── name.txt

Built-in classes

typedpath comes with a built-in collection of classes for representing directories and files, and you can create your own to support any additional types you need.

TextFile and BytesFile

The two most basic classes included in typedpath are TextFile and BytesFile, which allows you to read and write basic strs and bytess. Both come with read and write methods for accessing data:

tf = tp.TextFile("my_text.txt")
tf.write("Hello, world!")
print(tf.read())

bf = tp.BytesFile("my_bytes.bin")
bf.write(b"Hello, world!")
print(bf.read())

StructDir and passing arguments

The first class provided for composition is StructDir. A StructDir has a fixed number of members that may have different types. The members are declared using Python type hints:

class Person(tp.StructDir):
    name: tp.TextFile
    config: tp.JSONFile


class Database(tp.StructDir):
    people: tp.DictDir[str, Person]

All members should be a subclass of tp.TypedPath, and the name of the member becomes the name of the file on the filesystem.

Some members may require configuration that is not (easily) expressible in the type system. For example TextFile can take an encoding argument. To pass such arguments to the members you can use the withargs function:

class Person(tp.StructDir):
    name: tp.TextFile = tp.withargs(encoding="ascii")
    config: tp.JSONFile


p = Person("person")
p.name.write("Eve")

DictDir and key encoding

The other class provided for composition is DictDir. The DictDir has a variable number of members, but they must all have the same type. As the name implies the DictDir mimics a Python dict, mapping filenames to typedpath objects.

If a DictDir is created as part of a StructDir the types of the keys and values are determined from the type annotations in the StructDir. If you create a free-standing DictDir you must pass the type of the keys and values to __init__:

people = tp.DictDir("people", str, Person)

You can use the value_args keyword-argument to pass arguments to the children:

configs = tp.DictDir("configs", str, tp.TextFile, value_args=tp.withargs(encoding="ascii"))

By default DictDir uses str to convert the keys into a filename, and the key types __init__ to convert filenames back into key objects. If that does not work for the type you would like to use for keys, you can implement a KeyCodec for converting between your keys and strings:

from typing import Type

class BoolKeyCodec(tp.KeyCodec[bool]):
    def encode(self, key: bool) -> str:
        return "True" if key else "False"

    def decode(self, key_str: str, key_type: Type[bool]) -> bool:
        assert issubclass(key_type, bool), key_type
        match key_str:
            case "True":
                return True
            case "False":
                return False
        raise AssertionError(f"Don't know how to interpret {key_str} as a bool")

Then register your codec for default use in all DictDirs:

tp.add_key_codec(bool, BoolKeyCodec())

Or you can set which KeyCodec to use in just one specific DictDir:

bools = tp.DictDir("bools", bool, tp.TextFile, key_codec=BoolKeyCodec())

JSON support

typedpath provides JSONFile for reading and writing using Python's built-in json module:

json = tp.JSONFile("example.json")
json.write(
    {
        "is_example": True,
        "example_names": ["alice", "bob", "eve"],
    }
)
print(json.read())

Pickle support

For pickling objects typedpath provides the PickleFile class. It takes a parameter for which type of object to (de)serialize:

class A:
    def __init__(self, value: int) -> None:
        self.value = value

    def talk(self) -> None:
        print(self.value)

pf = tp.PickleFile("a.pickle", A)
pf.write(A(13))
pf.read().talk()

If used with a StructDir the type hint defines the kind of object to (de)serialize:

class MyDir(tp.StructDir):
    a: tp.PickleFile[A]
    b: tp.TextFile


md = MyDir("my_dir")
md.a.write(A(42))
md.a.read().talk()

NumPy support

typedpath also provides (admittedly limited) classes for reading and writing NumPy arrays. NpyFile allows you to store a single array in a single file, and NpzFile does the same, but with compression:

import numpy as np

npy = tp.NpyFile("array.npy")
npy.write(np.array([1, 2, 3]))
print(npy.read())

npz = tp.NpzFile("array.npz")
npz.write(np.array([1, 2, 3]))
print(npz.read())

Pandas support

typedpath has a couple of classes for reading and writing Pandas data frames, supporting .csv, .feather and .parquet files:

import pandas as pd

df = pd.DataFrame(
    {
        "a": [1, 2, 3],
        "b": [True, False, True],
    }
)

csv = tp.PandasCsvFile("df.csv")
csv.write(df)
print(csv.read())

feather = tp.PandasFeatherFile("df.feather")
feather.write(df)
print(feather.read())

parquet = tp.PandasParquetFile("df.parquet")
parquet.write(df)
print(parquet.read())

Declaring your own classes

Obviously typeddict only provides a very small subset of the file types you may want to read and write. It is expected you will need to write you own classes to support further file types. To integrate with the typedpath framework your classes must:

1. If it is a file it should extend tp.TypedFile. If it is a directory it should extend tp.TypedDir.

2. You class should have a static member variable called default_suffix defining what the suffix of these objects normally is. It can be empty ("").

3. In simple cases do not define __init__. If you need to define __init__ it must have: self; the filesystem path this object represents, with type tp.PathLikeLike; then any generic type arguments this class may need; and finally any keyword arguments your class needs for configuration.

4. To write to a file use self.write_path() to access the path. This method ensures any parent directories are created.

5. To read from a file use self.read_path() to access the path. This method ensures the path already exists.

6. To do anything else with the path, use self.pretty_path().

7. Other than that, add any methods you feel you need to read/write data.

Generally the template is:

class <YourClassName>(TypedFile):
    default_suffix = "<your suffix>"

    def __init__(
        self,
        path: PathLikeLike,
        <any generic type arguments go here>,
        *,
        <kwargs for configuration>
    ) -> None:
        super().__init__(path)

        <initialize stuff here>

    def write(self, ...) -> None:
        <write to self.write_path() here>

    def read(self) -> ...:
        <read from self.read_path() here>

For example, here's the implementation of TextFile:

class TextFile(TypedFile):
    default_suffix = ".txt"

    def __init__(self, path: PathLikeLike, *, encoding: str = "utf-8") -> None:
        super().__init__(path)

        self._encoding = encoding

    def write(
        self,
        data: str,
        *,
        errors: str | None = None,
        newline: str | None = None,
    ) -> int:
        return self.write_path().write_text(
            data, encoding=self._encoding, errors=errors, newline=newline
        )

    def read(self, errors: str | None = None) -> str:
        return self.read_path().read_text(encoding=self._encoding, errors=errors)

And PickleFile (which is a generic class):

class PickleFile(TypedFile, Generic[T]):
    default_suffix = ".pickle"

    def __init__(self, path: PathLikeLike, value_type: Type[T]) -> None:
        super().__init__(path)

        self._value_type = value_type

    def write(self, data: T, **kwargs: Any) -> None:
        with open(self.write_path(), "wb") as fp:
            pickle.dump(data, fp, **kwargs)

    def read(self, **kwargs: Any) -> T:
        with open(self.read_path(), "rb") as fp:
            result: T = pickle.load(fp, **kwargs)
            origin = get_origin(self._value_type)
            if origin is not None:
                assert isinstance(result, origin)
            return result