Files

https://docs.python.org/3/library/functions.html#open

INTRODUCTION

Python distinguishes between binary and text I/O.

Files opened in binary mode ('mode' with 'b) return contents as bytes objects without any decoding.

Files opened in text mode ('mode' with 't', the default) return contents as string where bytes are decoded using 'encoding'. A text file content can be divided onto lines ending with '\n'. Note that the last line may be without '\n'.

'open()' returns a 'file object', and is most commonly used with two arguments: open(filename, mode). Files opened for processing should be closed as soon as possible.

# afile = open(filename, mode='r', buffering)   # Py2
# afile = open(filename, mode='r', buffering=-1, encoding=None, errors=None,
#    newline=None, closefd=True, opener=None)   # Py3
# filename : a path-like object giving the pathname
# mode : a string that specifies the mode in which the file is opened
# encoding : used in text mode, usually 'utf-8'

# Available modes (character - meaning):
# 'r' - open for reading (default)
# 'w' - open for writing, truncating the file first
# 'x' - open for exclusive creation, failing if the file already exists
# 'a' - open for writing, appending to the end of the file if it exists
# 'b' - binary mode
# 't' - text mode (default)
# '+' - open for updating (reading and writing)

READING TEXT FILES

infile = open("book.txt", "r")   # default text mode, Py2 an Py3
#infile = open('book.txt', 'r', encoding='utf-8')   # Py3

S = infile.read(3)   # read 3 code points
#S = infile.read()   # read all, problems with large files!
#S = infile.readline()   # read a line with '\n'

print(S)   # print() adds '\n'
infile.close()

infile = open("book.txt", "r")   # default text mode

#L = infile.readlines()   # list of lines with '\n'
L = infile.readlines(50)   # list of lines, 50 or more code points

print(L)
infile.close()

infile = open("book.txt", "r")   # default text mode

for line in infile:   # 'line' with '\n'
    print(line, len(line))

infile.close()

infile = open('book.txt', 'r')   # default text mode

while True:
    text = infile.read(3)
    print(text)
    if text == "":
        break

infile.close()

# Using a context manager (recommended).

with open('book.txt', 'r') as infile:   # infile will be closed
    text = infile.read()

print(text)

WRITING TEXT FILES

outfile = open('results.txt', 'w')   # default text mode, Py2 an Py3
#outfile = open('results.txt', 'w', encoding='utf-8')   # Py3

n = 53
word = "żarówka"   # 7 code points ('bulb' in English)

outfile.write("{}\n{}\n".format(n, word))   # 2 lines

# outfile.write(str(n))
# outfile.write("\n")
# outfile.write(word)
# outfile.write("\n")

outfile.close()

outfile = open('results.txt', 'w')

n = 53
word = "żarówka"   # 7 code points ('bulb' in English)

L = ["{}\n".format(n), "{}\n".format(word)]   # list of lines with '\n'

outfile.writelines(L)

outfile.close()

# Using a context manager (recommended).

n = 53
word = "żarówka"   # 7 code points ('bulb' in English)

with open('results.txt', 'w') as outfile:   # outfile will be closed
    outfile.write("{}\n{}\n".format(n, word))   # 2 lines