py3streams 0.1.0

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py3streams - manipulate collections

Package contains classes to support operations on collection like set, list, dict or range using chain of generators.

Table of contents

• Description
• Installation
• Usage

Description

Classes from the package are: Stream, IntStream and DictStream. Classes are not collections but they are iterable. Only few methods executed stored lazy generators and evaluate result. Streams cannot be reused, chain of filters, maps and/or fmaps can be evaluated once. Filters, maps and fmaps do not invoke stream. After stream is invoked, stream cannot be reused. Methods which invoke stream are: to_list, to_dict, count, sum, max, min, any_match, all_match.

example_list = ["1", "5", "2", "10", "11"]
sum = Stream(example_list).map_to_int().filter(lambda x: x < 10).sum()
# result: [1, 5, 2] -> 8

In the example class Stream has been used on the example_list. First there is registered generator for changing strings to ints, then registered generator with lambda expression for elements lower than 10 and sum them.

Classes Stream, IntStream and DictStream hold provided collection as an iterable object and generators which are related with filter(s) and map(s) methods for future lazy evaluation.

Iteration example

Streams can be used with python for-loop.

for element in IntStream(1, 9).filter(lambda x: x % 2 == 0):
    print(element)
# result: 2, 4, 6 and 8

Installaton

To use the streams install the package.

pip install py3stream

Usage

Streams help manipulate collections. For most actions its enough to use filter(), map() and fmap() methods. Classes contain build-in functions which include lambdas and allow use short-name methods for similar result.

Example 1

Lets define a list

elements = [0, 1, "2", 3, None, [5, 6, "7"], ["8"]]

Stream will find elements lower than 3. Sub-lists and None values should be ignored. Class stream can be created like:

stream = Stream(elements).filter(lambda x: x is not None).filter(lambda x: not isinstance(x, list)).map(lambda x: int(x)).filter(lambda x: x < 3) # still we have a stream 
for e in stream:
    print(e)
# result 0, 1 and 2

and alternative with Stream's functions:

stream = Stream(elements).no_list().no_none().map_to_int().lt(3)
for e in stream:
    print(e)
# result 0, 1 and 2

Example 2

Lets define a list

elements = ["a", "b", 3, 4]

Stream will find first int

value = Stream(elements).filter(lambda x: isinstance(x, int)).get_first()
# result 3

get_first(default_value=None) returns None if Stream does not find element by default.

value = Stream(elements).filter(lambda x: isinstance(x, list)).get_first(5)
# result is 5