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Python: filter() function

filter() function

The filter() function construct an iterator from those elements of iterable for which function returns true.

Version:

(Python 3.2.5)

Syntax:

filter(function, iterable)

Parameter:

Name Description
function A Function to be run to test if elements of an iterable returns true or false. If function is None, the identity function is assumed, that is, all elements of iterable that are false are removed.
iterable

iterable may be either a sequence, a container which supports iteration, or an iterator.

Example: Python filter() function

# list of alphabets
letters = ['a', 'b', 'd', 'e', 'p', 'j', 'i','s', 'o', 'r', 'u']

# function that filters non-vowels
def filter_non_vowels(letters):
    vowels = ['a', 'e', 'i', 'o', 'u']

    if(letters in vowels):
        return False
    else:
        return True 

filter_non_vowels = filter(filter_non_vowels, letters)

print('The filtered non-vowels are:')
for non_vowel in filter_non_vowels:
    print(non_vowel)

Output:

The filtered non-vowels are:
b
d
p
j
s
r

Pictorial Presentation:

Python: Built-in-function - filter() function

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Python: Tips of the Day

Find current directory and file's directory:

To get the full path to the directory a Python file is contained in, write this in that file:

import os 
dir_path = os.path.dirname(os.path.realpath(__file__))

(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)

To get the current working directory use

import os
cwd = os.getcwd()

Documentation references for the modules, constants and functions used above:

  • The os and os.path modules.
  • The __file__ constant
  • os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")
  • os.path.dirname(path) (returns "the directory name of pathname path")
  • os.getcwd() (returns "a string representing the current working directory")
  • os.chdir(path) ("change the current working directory to path")

Ref: https://bit.ly/3fy0R6m