File Operations in Python

Internal

• Python Code Examples
• os

Check whether a File Exists

os.path

import os.path
file_exists = os.path.exists(path_to_file)

Returns True or False.

pathlib

Path represents a filesystem path that offers methods to do system calls on path objects. Depending on your system, instantiating a Path will return either a PosixPath or a WindowsPath object. You can also instantiate a PosixPath or WindowsPath directly, but cannot instantiate a WindowsPath on a POSIX system or vice versa.

from pathlib import Path
path = Path(path_to_file)
path.is_file()

New Path instance can be constructed from a Path instance:

path = Path('.')
path2 = Path(path, './some-file.txt')

Relative paths ("../../..") can be "resolved" with:

path = Path('/Users/ovidiu/..')
print(path.resolve()) # will display "/Users"

Reading/Writing from/to Files

Read

Understand this idiom. What does with do? Does it automatically close the file when it exits the block? Apparently this is a "context manager".

with open('somefile.txt', 'rt') as f:
  text = f.read()
  print(text)

 f = open(''filename'', ''mode'')
 c = f.read()
 f.close()

f = open('somefile', 'rt')
c = f.read()
f.close()

Mode: "r", "w", "x", etc. "t" text, "b" binary

Write

f = open('/Users/ovidiu/tmp/out.json', 'wt')
f.write("test\n")
f.close()

Working Directory

import os
print('getcwd:', os.getcwd())

Also see:

os

The Path of the Running Script File

print('__file__:', __file__)

Paths

os.path.basename returns the file name from the file path:

import os
print(os.path.basename(__file__))

os.path.dirname returns the directory name from the file path.

import os
print(os.path.dirname(__file__))

os.path.abspath return the absolute path from a file path.

os.path.splittext returns the file name from the file path.

Use the pathlib module to extract directory name.

Removing Files

import os
os.remove("somefile.txt")
os.rmdir("somedir") # removes an empty directory
shutil.rmtree() # deletes a directory and all its contents.

Path objects from the Python 3.4+ pathlib module also expose these instance methods:

pathlib.Path.unlink()  # removes a file or symbolic link.
pathlib.Path.rmdir() # removes an empty directory.

Temporary Files

https://docs.python.org/3/library/tempfile.html

Create a named temporary file, write in it and return the name. The file is not automatically deleted after close(), the caller will need to delete it:

import tempfile
with tempfile.NamedTemporaryFile(mode='w+t', delete=False) as t:
  t.write(something)
  return t.name