learn-python/src/files/test_file_methods.py at master · joseville14/learn-python · GitHub

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"""Methods of File Objects

@see: https://docs.python.org/3/tutorial/inputoutput.html#methods-of-file-objects

Reading from a file does not always have to be sequential. There are methods to look for

specific locations in the file, much like flipping to a page in a book.

"""

def test_file_methods():

"""Methods of File Objects"""

multi_line_file = open('src/files/multi_line_file.txt', 'r')

binary_file = open('src/files/binary_file', 'r')

# To read a file’s contents, call f.read(size), which reads some quantity of data and returns

# it as a string (in text mode) or bytes object (in binary mode). size is an optional numeric

# argument. When size is omitted or negative, the entire contents of the file will be read and

# returned; it’s your problem if the file is twice as large as your machine’s memory. Otherwise,

# at most size bytes are read and returned. If the end of the file has been reached, f.read()

# will return an empty string ('').

read_data = multi_line_file.read()

# pylint: disable=duplicate-code

assert read_data == 'first line\nsecond line\nthird line'

# To change the file object’s position, use f.seek(offset, from_what). The position is computed

# from adding offset to a reference point; the reference point is selected by the from_what

# argument. A from_what value of 0 measures from the beginning of the file, 1 uses the current

# file position, and 2 uses the end of the file as the reference point. from_what can be omitted

# and defaults to 0, using the beginning of the file as the reference point.

assert binary_file.seek(0) == 0 # Go to the 0th byte in the file

assert binary_file.seek(6) == 6 # Go to the 6th byte in the file

assert binary_file.read(1) == '6'

# f.readline() reads a single line from the file; a newline character (\n) is left at the end

# of the string, and is only omitted on the last line of the file if the file doesn’t end in a

# newline. This makes the return value unambiguous; if f.readline() returns an empty string,

# the end of the file has been reached, while a blank line is represented by '\n', a string

# containing only a single newline.

multi_line_file.seek(0)

assert multi_line_file.readline() == 'first line\n'

assert multi_line_file.readline() == 'second line\n'

assert multi_line_file.readline() == 'third line'

assert multi_line_file.readline() == ''

multi_line_file.close()

binary_file.close()

learn-python/src/files/test_file_methods.py at master · joseville14/learn-python · GitHub

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