The filter function in Python

The filter () function is another useful high-order function built into Python, and the filter () function receives a function f and a list, the function F of which is to judge each element, returning True or False,filter () Automatically filters out non-conforming elements based on the result of the decision, returning a new list of eligible elements.

For example, to delete an even number from a list [1, 4, 6, 7, 9, 12, 17] and keep an odd number, first, write a function that judges the odd number:

def is_odd (x):    return x% 2 = = 1

Then, filter out the even number using filter ():

>>>filter (Is_odd, [1, 4, 6, 7, 9, 12, 17])

Results:

[1, 7, 9, 17]

With filter (), you can accomplish many useful functions, such as deleting None or an empty string:

def is_not_empty (s):    return S and Len (S.strip ()) > 0>>>filter (is_not_empty, [' Test ', None, ' ', ' str ', ' 
    ', ' END '])

Results:

[' Test ', ' str ', ' END ']

Note: S.strip (RM) Deletes the characters of the RM sequence at the beginning and end of the S string.

When RM is empty, the default is to remove the white space character (including ' \ n ', ' \ R ', ' \ t ', '), as follows:

>>> a = ' 123 '
>>> A.strip ()
' 123 '

>>> a = ' \t\t123\r\n '
>>> A.strip ()
' 123 '

Practice:

Filter () to 1~100 that the square root is an integer number, i.e. the result should be:

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

Method:

Import Mathdef IS_SQR (x):    return math.sqrt (x)% 1 = = 0print Filter (IS_SQR, Range (1, 101))

Results:

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

The filter function in Python