File Operations in Python

Internal

• Python Code Examples
• os
• shutil

TODO

• TO PROCESS PyOOP "File I/O" + "Placing it in context"
• TO PROCESS PyOOP "Filesystem paths"

Check whether a File Exists

Use either or pathlib exists(), is_file(), is_dir() or os.path.exists().

Reading/Writing from/to Files

The open() Built-in

open() is a built-in function.

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.

Recursively Copy a Directory

Recursively Copy a Directory with shutil

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

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.

New Path instance can be constructed from a Path instance:

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

Convert the Path to a string with str():

path = Path('.')
print(str(path))

Accessing the File Name

Path('...').name

Accessing the Parent

Path('...').parent

resolve(strict=False)

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

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

mkdir(mode=0o777, parents=False, exist_ok=False)

Create a directory, including its non-existent parents if required.

d = Path('somedir')
d.mkdir(0o700, True, False)

Setting parents to True will create intermediate missing directories if necessary. By default, parents is False.

The method fails if the directory already exists, unless exist_ok is set to True.

exists(), is_file(), is_dir()

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

rmdir()

from pathlib import Path
path = Path(path_to_dir)
path.rmdir()

The directory must be empty. shutil has a function that deletes the directory recursively.

iterdir()

Iterate over the files in this directory. Does not yield any result for the special paths '.' and '..'.

from pathlib import Path
path = Path(path_to_dir)
for f in path.iterdir():
  ...

Other pathlib Methods

• cwd()
• home()
• samefile(other_path)
• glob(pattern)
• rglob(pattern)
• absolute()
• stat()
• group()
• open(mode='r', buffering=-1, encoding=None, errors=None, newline=None)
• read_bytes()
• read_text(encoding=None, errors=None)
• write_bytes(data)
• write_text(data, encoding=None, errors=None)
• touch(mode=0o666, exist_ok=True)
• chmod(mode)
• lchmod(mode)
• unlink(missing_ok=False)
• lstat()
• link_to(target)
• rename(target)
• replace(target)
• symlink_to(target, target_is_directory=False)
• is_mount()
• is_symlink()
• is_block_device()
• is_char_device()
• is_fifo()
• is_socket()
• expanduser()

os.path

exists(path_to_file)

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

Returns True or False.