Let's speed that file sentence searching program
Yay, PEP 8

72 characters for docstrings, 79 for the code. The rest seems fine.

Separation of concerns

search_sentence_in_file should search, and return its results. Not print, it is the duty of the caller.

I feel it is also wrongly named as it search a sentence in several files. So at least add the missing s at the end of the name. And to make it even more reusable, why not pass an iterable of filepath (like the get_magic_files generator)?

Genericity

Besides search_sentence_in_file accepting an iterable, you could make get_magik_files more generic by passing the required extension as a parameter. This will let you extend your script to allow search in various kind of files.

First rewrite

from os import walk
from os.path import join, splitext


def get_files(base_path, extension=None):
    """
    Yields each path from all the base_path subdirectories

    :param base_path: this is the base path from where the
                      function start looking for relevant files
    :param extension: filter files using provided extension.
                      If None, no filter is applied.
    :return: yield full path of a requested file
    """
    if extension is None:
        def filter_files(filenames):
            yield from filenames
    else:
        def filter_files(filenames):
            for filename in filenames:
                if splitext(filename)[1] == extension:
                    yield filename

    for dirpath, _, filenames in walk(base_path):
        for filename in filter_files(filenames):
            yield join(dirpath, filename)


def search_sentence_in_files(files, sentence):
    """
    Yield each file path, line and line content where
    sentence was found.

    :param files: iterable of files to search the sentence into
    :param sentence: the sentence we're looking up for
    :return: yield the file path, line number and line
             content where sentence was found
    """
    for filepath in files:
        with open(filepath) as fp:
            for line_number, line in enumerate(fp):
                if sentence in line:
                    yield filepath, line_number, line.strip()


def main():
    basepath = r'some_path'
    sentence_to_search = 'some sentence'

    files = get_files(basepath, 'magik')
    results = search_sentence_in_files(files, sentence_to_search)
    for filepath, line, content in results:
        print('[# FILE PATH    #]', filepath, '...')
        print('[# LINE NUMBER  #] At line', line)
        print('[# LINE CONTENT #] Content:', content)
        print('-'*80)


if __name__ == '__main__':
    main()


Reusability

Your script make it hard to reuse for other purposes: different sentences, different kind of files. Better to add a CLI using argparse. Provide sensible default for your current usage but allows for customization at will.

from os import walk
from os.path import join, splitext
import argparse


def get_files(base_path, extension=None):
    """
    Yields each path from all the base_path subdirectories

    :param base_path: this is the base path from where the
                      function start looking for relevant files
    :param extension: filter files using provided extension.
                      If None, no filter is applied.
    :return: yield full path of a requested file
    """
    if extension is None:
        def filter_files(filenames):
            yield from filenames
    else:
        def filter_files(filenames):
            for filename in filenames:
                if splitext(filename)[1] == extension:
                    yield filename

    for dirpath, _, filenames in walk(base_path):
        for filename in filter_files(filenames):
            yield join(dirpath, filename)


def search_sentence_in_files(files, sentence):
    """
    Yield each file path, line and line content where
    sentence was found.

    :param files: iterable of files to search the sentence into
    :param sentence: the sentence we're looking up for
    :return: yield the file path, line number and line
             content where sentence was found
    """
    for filepath in files:
        with open(filepath) as fp:
            for line_number, line in enumerate(fp):
                if sentence in line:
                    yield filepath, line_number, line.strip()


def main(files, sentence):
    results = search_sentence_in_files(files, sentence)
    for filepath, line, content in results:
        print('[# FILE PATH    #]', filepath, '...')
        print('[# LINE NUMBER  #] At line', line)
        print('[# LINE CONTENT #] Content:', content)
        print('-'*80)


if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='Search text in files')
    parser.add_argument('sentence')
    parser.add_argument('-p', '--basepath',
                        help='folder in wich files will be examinated',
                        default=r'some folder')
    parser.add_argument('-e', '--extension',
                        help='extension of files to examine',
                        default='magik')
    args = parser.parse_args()

    files = get_files(args.basepath, args.extension)
    main(files, args.sentence)


You can also allows for other improvements such as the sentence being a regular expression.