Installation

pip install funcy

Overview

Import stuff from funcy to make things happen:

from funcy import whatever, you, need

Merge collections of same type (works for dicts, sets, lists, tuples, iterators and even strings):

merge(coll1, coll2, coll3, ...)
join(colls)
merge_with(sum, dict1, dict2, ...)

Walk through collection, creating its transform (like map but preserves type):

walk(str.upper, {'a', 'b'})            # {'A', 'B'}
walk(reversed, {'a': 1, 'b': 2})       # {1: 'a', 2: 'b'}
walk_keys(double, {'a': 1, 'b': 2})    # {'aa': 1, 'bb': 2}
walk_values(inc, {'a': 1, 'b': 2})     # {'a': 2, 'b': 3}

Select a part of collection:

select(even, {1,2,3,10,20})                  # {2,10,20}
select(r'^a', ('a','b','ab','ba'))           # ('a','ab')
select_keys(callable, {str: '', None: None}) # {str: ''}
compact({2, None, 1, 0})                     # {1,2}

Manipulate sequences:

take(4, iterate(double, 1)) # [1, 2, 4, 8]
first(drop(3, count(10)))   # 13

lremove(even, [1, 2, 3])    # [1, 3]
lconcat([1, 2], [5, 6])     # [1, 2, 5, 6]
lcat(map(range, range(4)))  # [0, 0, 1, 0, 1, 2]
lmapcat(range, range(4))    # same
flatten(nested_structure)   # flat iter
distinct('abacbdd')         # iter('abcd')

lsplit(odd, range(5))       # ([1, 3], [0, 2, 4])
lsplit_at(2, range(5))      # ([0, 1], [2, 3, 4])
group_by(mod3, range(5))    # {0: [0, 3], 1: [1, 4], 2: [2]}

lpartition(2, range(5))     # [[0, 1], [2, 3]]
chunks(2, range(5))         # iter: [0, 1], [2, 3], [4]
pairwise(range(5))          # iter: [0, 1], [1, 2], ...

And functions:

partial(add, 1)             # inc
curry(add)(1)(2)            # 3
compose(inc, double)(10)    # 21
complement(even)            # odd
all_fn(isa(int), even)      # is_even_int

one_third = rpartial(operator.div, 3.0)
has_suffix = rcurry(str.endswith, 2)

Create decorators easily:

@decorator
def log(call):
    print(call._func.__name__, call._args)
    return call()

Abstract control flow:

walk_values(silent(int), {'a': '1', 'b': 'no'})
# => {'a': 1, 'b': None}

@once
def initialize():
    "..."

with suppress(OSError):
    os.remove('some.file')

@ignore(ErrorRateExceeded)
@limit_error_rate(fails=5, timeout=60)
@retry(tries=2, errors=(HttpError, ServiceDown))
def some_unreliable_action(...):
    "..."

class MyUser(AbstractBaseUser):
    @cached_property
    def public_phones(self):
        return self.phones.filter(public=True)

Ease debugging:

squares = {tap(x, 'x'): tap(x * x, 'x^2') for x in [3, 4]}
# x: 3
# x^2: 9
# ...

@print_exits
def some_func(...):
    "..."

@log_calls(log.info, errors=False)
@log_errors(log.exception)
def some_suspicious_function(...):
    "..."

with print_durations('Creating models'):
    Model.objects.create(...)
    # ...
# 10.2 ms in Creating models

And much more.

Dive in

Funcy is an embodiment of ideas I explain in several essays:

• Why Every Language Needs Its Underscore

• Functional Python Made Easy

• Abstracting Control Flow

• Painless Decorators

Related Projects

• https://pypi.org/project/funcy-chain/

• https://pypi.org/project/funcy-pipe/

Running tests

To run the tests using your default python:

pip install -r test_requirements.txt
pytest

To fully run tox you need all the supported pythons to be installed. These are 3.4+ and PyPy3. You can run it for particular environment even in absense of all of the above:

tox -e py310
tox -e pypy3
tox -e lint