Extension of Builtin Functions

Following extended versions of built-in functions are provided.

The function name may be sufficed with _ to avoid name conflict with Python keywords and built-in functions.

Callable Creators

calcpy.arggetter(*keys, default=Missing)

Return a callable object that fetches the argument(s) from its operand.

Parameters:

• *keys (int | str) – If it is an int (can be negative), it is the index of the positional argument to be fetched. If it is a str, it is the name of keyword argument to be fetched.

• default (optional) – Indicate how to return when an argument is not found. If not set, will raise an error when an argument is not found.

Return type:

callable

Raises:

IndexError – Raises when the argument is not found and the default is not set.

Examples

Get the first positional argument.

>>> getter = arggetter(0)
>>> getter("a", "b", "c", key="value")
'a'

Get the positional arguments and keyword arguments.

>>> getter = arggetter(-1, 0, 1, "key", default="default")
>>> getter("a", "b", "c", key="value")
('c', 'a', 'b', 'value')

Get the positional arguments and keyword arguments with default values.

>>> getter = arggetter(-1, 0, 1, 5, "key", "other", default="default")
>>> getter("a", "b", "c", key="value")
('c', 'a', 'b', 'default', 'value', 'default')

It will return the key if the key is not found.

>>> from calcpy.fun import skewer
>>> lookup = {"a": 1, "b": 2}
>>> g = skewer(arggetter(0, 0), lookup.get)  # equivalent to lookup.get(x, x)
>>> g("a")
1
>>> g("c")
'c'

Raise an error if the index is out of range and the default is not set.

>>> getter = arggetter(0, 1, 2)
>>> getter("A", key="value")
Traceback (most recent call last):
...
IndexError: positional argument index is out of range

calcpy.attrgetter(*attrs, default=Missing)

Return a callable object that fetches the given attribute(s) from its operand.

Fully compatible with Python’s built-in operator.attrgetter, and furthermore support an optional default value when a named attr is not found.

Parameters:

• *attrs (str) – Attribute names.

• default (optional) – Indicate how to return when a named attr is not found. If not set, will raise an error when an attribute is not found.

Examples

Get attributes with default values.

>>> from collections import namedtuple
>>> name = namedtuple('Name', ['first', 'last'])
>>> name.first = 'Zhiqing'
>>> name.last = 'Xiao'
>>> person = namedtuple('Person', ['name', 'city'])
>>> person.name = name
>>> person.city = 'Beijing'
>>> g = attrgetter('name.first', 'name.middle', 'name.last', default='')
>>> g(person)
('Zhiqing', '', 'Xiao')
>>> g = attrgetter('name.first', 'city')
>>> g(person)
('Zhiqing', 'Beijing')

It will raise errors when the default is not set.

>>> g = attrgetter('hello')
>>> g(sum)
Traceback (most recent call last):
...
AttributeError: type object 'builtin_function_or_method' has no attribute 'hello'

See also

https://docs.python.org/3/library/operator.html#operator.attrgetter

calcpy.itemgetter(*items, default=Missing)

Return a callable object that fetches the given item(s) from its operand.

Fully compatible with Python’s builtin operator.itemgetter, and furthermore support multi-level item and an optional default value when a item is not found.

Parameters:

• *items (str) – Keys of items.

• default (optional) – Indicate how to return when a named attr is not found. If not set, will raise an error when an item is not found.

Examples

Get multiple items with default values.

>>> person = {'name': {'first': 'Zhiqing', 'last': 'Xiao'}, 'city': 'Beijing'}
>>> g = itemgetter(['name', 'first'], ['name', 'middle'], ['name', 'last'], 'city', default='')
>>> g(person)
('Zhiqing', '', 'Xiao', 'Beijing')
>>> itemgetter(4, default=0)([1, 2, 3])
0

It will raise errors when the default is not set.

>>> itemgetter(4)([1, 2, 3])
Traceback (most recent call last):
...
IndexError: list index out of range

See also

https://docs.python.org/3/library/operator.html#operator.itemgetter

calcpy.methodcaller(name, *args, **kwargs)

Fully compatible with Python’s built-in operator.methodcaller.

Support pandas accessor.

Can be decorated by calcpy.fillerr when needed to resolve the case where method name is not found.

Examples

>>> import pandas as pd
>>> s = pd.Series(["a", "b"])
>>> methodcaller("str.upper")(s)
0    A
1    B
dtype: object

See also

https://docs.python.org/3/library/operator.html#operator.methodcaller

calcpy.constantcreator(value, /, copy=False)

Callable that returns the same constant when it is called.

Parameters:

• value – Constant value to be returned.

• copy – If True, return a new copy of the constant value.

Returns:

Callable object that returns value, ignoring its parameters.

Return type:

callable

Examples

Always return the string "value".

>>> creator = constantcreator("value")
>>> creator()
'value'

Create a pd.DataFrame whose elements are all empty lists.

>>> import pandas as pd
>>> df = pd.DataFrame(index=range(3), columns=["A"])
>>> (df.map if hasattr(df, "map") else df.applymap)(constantcreator([]))
    A
0  []
1  []
2  []

Return a new copy when copy=True.

>>> import pandas as pd
>>> df = pd.DataFrame(index=range(3), columns=["A"])
>>> constantcreator(df, copy=True)() is df
False

See also

https://extepy.github.io/builtin.html#extepy.constantcreator

Checkers

calcpy.argchecker(*keys)

Return a callable object to check the existences of argument(s).

Parameters:

*keys (int | str) – If it is an int (can be negative), it is the index of the positional argument to be fetched. If it is a str, it is the name of keyword argument to be fetched.

Return type:

bool | tuple[bool]

Examples

>>> getter = argchecker(-1, 0, 1, 5, "key", "other")
>>> getter("a", "b", "c", key="value")
(True, True, True, False, True, False)

calcpy.attrchecker(*attrs)

Return a callable object to check the existence of the given attribute(s).

Parameters:

*attrs (str) – Attribute names.

Examples

>>> c = attrchecker("mro", "type")
>>> c(type)
(True, False)

>>> import os
>>> c = attrchecker("path", "path.sep", "sep.path")
>>> c(os)
(True, True, False)

calcpy.itemchecker(*items)

Return a callable object to check the existence of the given item(s).

Examples

>>> data = {"name": {"first": "Zhiqing", "last": "Xiao"}, "city": "Beijing"}
>>> c = itemchecker(["name", "first"], ["name", "middle"], ["name", "last"], "city", "sex")
>>> c(data)
(True, False, True, True, False)

>>> itemchecker(-3, 0, 3)([1, 2, 3])
(True, True, False)