Table of Contents

• open
• readline
• When the buffer is flushed?
• Read a file except the first line

open

buffering

0

unbuffered (read and write are one system call and can return short)

1

line buffered (only usable if universal_newlines=True i.e., in a text mode)

any other positive value

use a buffer of approximately that size

negative bufsize (the default)

the default buffering policy as follows:

• binary files use io.DEFAULT_BUFFER_SIZE
• interactive text files(files for which isatty() returns True) use line buffering.
• In other words, even sys.stdout can be fully buffered if it runs as a background proces

Returns

• binary files are instances of BytesIO
• text files are instances of StringIO

readline

• f.readline() reads a single line from the file
• A newline character (\n) is left at the end of the string
• Handles whether or not the last line has a newline character
• A blank line is represented by \n

An useful idiom is:

with open('mydata.txt') as f:
    for line in iter(f.readline, ''):
        process_line(line)

# Following codes will block until the file is ready
for line in f:
    pass

ls = f.readlines()

When the buffer is flushed? discussion

• when the buffer gets too small for all pending data;
• when flush() is called;
• when a seek() is requested (for BufferedRandom objects);
• when the BufferedWriter object is closed or destroyed.

Read a file except the first line howto

with open(fname) as f:
    next(f)
    for line in f:
        #do something