The os module talks to the operating system: where you are, what's in a folder, and creating, renaming or removing directories — the plumbing behind organising datasets.

Where am I?

Python

import os
start = os.getcwd()              # current working directory
os.mkdir("project")              # create one folder
os.chdir("project")              # move into it
print(os.path.basename(os.getcwd()))   # project
os.chdir("..")                   # back to the parent
print(os.getcwd() == start)      # True

Function	Does
`os.getcwd()`	Current working directory
`os.chdir(path)`	Change directory (`..` = parent)
`os.listdir(path='.')`	Names of files and folders in a directory
`os.mkdir(path)`	Create one folder (parent must exist)
`os.makedirs(path, exist_ok=True)`	Create a whole chain of folders
`os.rmdir(path)`	Remove an empty folder
`os.rename(old, new)`	Rename or move
`os.remove(path)`	Delete a file
`os.path.join(a, b)`	Build a path with the right separator
`os.path.exists(p)` / `isdir` / `isfile`	Check what's there

Nested folders

Python

import os
os.makedirs("data/raw/2026", exist_ok=True)     # creates data, data/raw and data/raw/2026
os.rmdir("data/raw/2026")                       # only works because it's empty
os.rename("data", "dataset")
print(sorted(os.listdir("dataset")))            # ['raw']

Creating folders in bulk

Python

import os
master = "KT"
n, m = 5, 5
for i in range(1, n + 1):
    for j in range(1, m + 1):
        os.makedirs(os.path.join(master, f"{master} {i}", f"{master} {i}.{j}"), exist_ok=True)

total = sum(len(dirs) for _, dirs, _ in os.walk(master)) + 1   # + the master folder itself
print(total)                                                    # 31

Reading many text files

Python

import os
os.makedirs("Files", exist_ok=True)
for name, text in [("a.txt", "first"), ("b.txt", "second"), (".DS_Store", "junk")]:
    with open(os.path.join("Files", name), "w") as f:
        f.write(text)

contents = []
for name in sorted(os.listdir("Files")):
    if name.startswith("."):                    # skip hidden files like .DS_Store
        continue
    with open(os.path.join("Files", name)) as f:
        contents.append(f.read())
print(contents)                                 # ['first', 'second']