Shulou(Shulou.com)06/01 Report--

This article mainly introduces the four functions of the itertools library in Python and how to use the relevant knowledge, the content is detailed and easy to understand, simple and fast operation, with a certain reference value, I believe that you read this Python in the four functions of the itertools library and how to use the article will have a harvest, let's take a look at it.

1. Introduction

In Python development, the itertools library is often overlooked, but it actually hates some great functions, especially those that are in the data stream.

2. Accumulate () function

The function accumulate () provided by the third-party library itertools can help us perform cumulative operations on data streams. In other words, let's say we have a list of data [arecine bdje] and an operation f, then the function accumulate () can help us to calculate f (aforce b), f (f (aforce b), c), f (a) b), c), d), and so on.

The text is a little unintuitive, so let's give a cumulative chestnut.

The sample code is as follows:

Import itertoolsdata = [3, 4, 6, 2, 1, 9, 0, 7, 5, 8] res = itertools.accumulate (data, lambda x) print (list (res)) [3, 7, 13, 15, 16, 25, 25, 32, 37, 45]

The function accumulate () above is to add 3 and 4, then get 7, then add 6 to get another value, and so on.

It is important to note that this function is not allowed if you want to perform an accumulative operation given three or more values, because accumulate () only accepts iterators, which return up to 1 element at a time when next () is called.

3. Compress () function

The function compress () filters the content according to our preferences. Unlike the function filter () function, the function compress () needs to pass in the corresponding flag bit to determine whether each value should be retained.

For example, it will be more intuitive, and the relevant sample code is as follows:

Import itertoolsdata = [3,4,6,2,1,9,0,7,5,8] selector = [1,0,0,0,1,1,0] res = itertools.compress (data, selector) print (list (res)) # [3,1,9,7,5]

In the above example, if the data is odd, the selector will be 1, otherwise 0. Therefore, the result of the function compress () operation will only retain the odd numbers in the original data.

4. Groupby () function

In many cases, we get a list of tuples in random order in Python, if we want to group them by value. This is the perfect scenario for the function groupby () to work!

The function groupby () will take an iterable argument and a function that returns a value, and then it will group the list of tuples by the value returned by the function.

For example, we want to group the following cities by country:

Import itertoolsdata = [('New York',' US'), ("Shanghai", "China"), ("LA", 'US'), ("Chongqing", "China")] for city, group in itertools.groupby (sorted (data, key=lambda x: X [1]), lambda x: X [1]): for i in group:print ("% s is in% s."% (I [0]) City) print (") # Shanghai is in China.# Chongqing is in China.# New York is in US.# LA is in US.5. Permutation and combination operation

Permutation and combination is probably one of the most amazing functions in the itertools library, which provides permutation and combination operators!

The only thing we need to do is pass the correct keyword to the corresponding function along with the length of the output tuple.

As shown in the following example:

Import itertoolsdata = [3,4,6] com_res = itertools.combinations (data, 2) print (list (com_res)) # [(3,4), (3,6), (4,6)] com_res = itertools.permutations (data, 2) print (list (com_res)) # [(3,4), (3,6), (4,3), (4,6), (6,3), (6) 4)] com_without_replacement_res = itertools.combinations_with_replacement (data, 2) print (list (com_without_replacement_res)) # [(3,3), (3,4), (3,6), (4,4), (4,6), (6,6)] product_res = itertools.product (data, data) print (list (product_res)) # [(3,3), (3,4), (3,6), (4,3) (4, 4), (4, 6), (6, 3), (6, 4), (6, 6)] this is the end of the article on "what are the four functions of itertools Library in Python and how to use them?" Thank you for reading! I believe you all have a certain understanding of the knowledge of "what are the four functions of the itertools library in Python and how to use them". If you want to learn more, you are welcome to follow the industry information channel.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.