Os

import os

os.chdir(path) #cd
cwd = os.getcwd() #pwd

Get all files in subdirs

for root, dirs, files in os.walk(PATH_TO_NOTES):
  for file in files:
    curFile = os.path.join(root, file)

Get Environment

os.environ.get('SECRET_KEY')

Files

Underlying open is from io library

#f is file object
f = open('workfile', 'w')
f.write("Now the file has one more line!")
f.close()
  
#To write bytes
with open(filename, 'wb') as f: 
  f.write(filebytes)

Modes

• 'r' read; DEFAULT

• 'w' writing(erase existing file)

• 'w+' writing(create new file if it doesn't exist)

• 'a' appending to the end

• 'a+' appending to the end(create new file if needed)

• 'r+' both reading and writing

Reading Data

for line in f:
    print(line)
    
f.readline()#leaves \n and '' when done

With

Automatically close for ya

with open('workfile', 'r') as f:
  read_data = f.read() #all datadddddd

Pickle

with open(r"categorizationModel.pickle", "wb") as output_file:
    cPickle.dump(rf, output_file)

with open(r"categorizationModel.pickle", "r") as model:
    rfLoaded = cPickle.load(model)

CPickle

• optimized cousin cPickle written in C, 1000x faster

• just doesn't support subclassing of the Pickler() and Unpickler() classes

• usually better

• same interface

Advanced OS*

• could bypass system caches, more metadata/permissions access

import os, fcntl


fd = os.open("file.txt", os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o644) #This creates a new file with specific permissions, failing if the file already exists

#Lock file
fd = os.open("file.txt", os.O_RDWR)
fcntl.flock(fd, fcntl.LOCK_EX)
# Perform operations...
fcntl.flock(fd, fcntl.LOCK_UN)
os.close(fd)

Play Audio Files

os.system("afplay Endgame.mp3")