atpalmer-python / python-monkeypatch

Ruby-like monkeypatching on Python's built-in types

monkeypatch

The monkeypatch package provides an interface to add user-defined methods to built-in types.

The wish!

Sadly, in Python, this code raises TypeError: can't set attributes of built-in/extension type 'str':

    str.hello = "world"

Although you can easily add attributes to your custom types, modifying built-in types, like str, is usually off-limits in Python.

Until now...

Examples

Here are some interesting possibilities:

Add a str method to, say, reverse and uppercase strings:

    from monkeypatch import monkeypatch

    def rev_up(self):
        return self[::-1].upper()

    monkeypatch(str, "rev_up", rev_up)

    assert "abc".rev_up() == "CBA"

Add a method to Python's int to work like Ruby's upto:

    from monkeypatch import monkeypatch

    def upto(self, value):
        return tuple(range(self, value + 1))

    monkeypatch(int, "upto", upto)

    assert (1).upto(10) == (1,2,3,4,5,6,7,8,9,10)

Add a method to tuple to multiply all items by some value:

    from monkeypatch import monkeypatch

    def mult_by(self, value):
        return tuple(x * value for x in self)

    monkeypatch(tuple, "mult_by", mult_by)

    assert (1,2,3).mult_by(10) == (10,20,30)