2.1 os

Important

This lesson is still under development.

When python is installed, several modules/packages are pre-installed in it. These modules provide some very basic functionality to the user. The os is such a built-in module which provides the functionalities about paths or operating system.

import os

system()

It is used to execute commands that we would otherwise execute using command prompt on windows or on terminal. For example on Windows we can do os.system(dir) where dir is a command for Windows command prompt

os.system(dir)

getcwd()

It returns the current working directory.

print(os.getcwd())

/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/builtin_modules

print(type(os.getcwd()))

<class 'str'>

path

The path submodule of os module contains several helpful functions to manipulate path.

Find out whether the path p exists or not

p = os.getcwd()
os.path.isdir(p)

True

Find out whther p is a file or not

os.path.isfile(p)

False

—

# Find the parent directory of `p`.
os.path.dirname(p)

'/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts'

—

os.path.abspath(p)

'/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/builtin_modules'

---

os.path.split(p)

('/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts', 'builtin_modules')

—

os.path.basename(p)

'builtin_modules'

—

os.path.exists(p)

True

remove()

delete a file from disk

replace()

listdir

Returns a list of folders/directories in a given path.

os.listdir(p)

['readme.txt', '_os.py', '_types_typing.py', '_csv.py', '_warnings.py', '_random_module.py', '_time.py', '_pathlib.py', '_sys.py', '_copy.py', '_collections.py', '_itertools.py', '_math.py']

environ

environ = os.environ
print(environ)
print(type(environ))
print(len(environ))

environ({'READTHEDOCS_VIRTUALENV_PATH': '/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/envs/dev', 'READTHEDOCS_CANONICAL_URL': 'https://python-seekho.readthedocs.io/en/dev/', 'HOSTNAME': 'build-26236814-project-717928-python-seekho', 'READTHEDOCS_GIT_CLONE_URL': 'https://github.com/AtrCheema/python-seekho.git', 'HOME': '/home/docs', 'NO_COLOR': '1', 'READTHEDOCS': 'True', 'READTHEDOCS_PRODUCTION_DOMAIN': 'readthedocs.org', 'READTHEDOCS_REPOSITORY_PATH': '/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev', 'READTHEDOCS_PROJECT': 'python-seekho', 'READTHEDOCS_OUTPUT': '/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/_readthedocs/', 'PATH': '/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/envs/dev/bin:/home/docs/.asdf/shims:/home/docs/.asdf/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin', 'READTHEDOCS_VERSION_TYPE': 'branch', 'LANG': 'C.UTF-8', 'READTHEDOCS_LANGUAGE': 'en', 'DEBIAN_FRONTEND': 'noninteractive', 'READTHEDOCS_GIT_COMMIT_HASH': 'ebaff922615a23925da260d6ea0b38c967ed6ee6', 'READTHEDOCS_VERSION_NAME': 'dev', 'READTHEDOCS_VERSION': 'dev', 'PWD': '/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/docs/source', 'READTHEDOCS_GIT_IDENTIFIER': 'dev', 'DOCUTILSCONFIG': '/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/docs/source/docutils.conf'})
<class 'os._Environ'>
22

wait()

rename()

renames()

mkdir()

creates a directory if all its upper/parent directories are present.

new_folder = os.path.join(os.getcwd(), "NewFolder")

print(os.path.exists(new_folder))
os.mkdir(new_folder)

print(os.path.exists(new_folder))

False
True

p = os.path.join(os.getcwd(), "NonExistentFolder", "InsideNonExistentFolder")

print(os.path.exists(p))

False

uncomment following line

# os.mkdir(p)  # FileNotFoundError

os.makedirs

os.makedirs(p)
print(os.path.exists(p))

True

rmdir()

print(os.path.exists(new_folder))
os.rmdir(new_folder)
print(os.path.exists(new_folder))

True
False

cpu_count()

Cound the number of cpus/cores/processes available.

print(os.cpu_count())

2

chdir()

original_wd = os.getcwd()
print("Current working directory is \n", original_wd)
print(f"It has {len(os.listdir(os.getcwd()))} sub-directories/folders in it.")
new_wd = os.path.join(os.path.dirname(original_wd))
os.chdir(new_wd)
print("Now we have changed working directory to \n", new_wd)
print(f"This new directory has {len(os.listdir(os.getcwd()))} sub-directories/folders in it")
# now changing back to original
os.chdir(original_wd)

Current working directory is
 /home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/builtin_modules
It has 14 sub-directories/folders in it.
Now we have changed working directory to
 /home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts
This new directory has 8 sub-directories/folders in it

walk

for dirpath, dirnames, filenames in os.walk(os.getcwd()):
    print(dirpath, dirnames, filenames)

/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/builtin_modules ['NonExistentFolder'] ['readme.txt', '_os.py', '_types_typing.py', '_csv.py', '_warnings.py', '_random_module.py', '_time.py', '_pathlib.py', '_sys.py', '_copy.py', '_collections.py', '_itertools.py', '_math.py']
/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/builtin_modules/NonExistentFolder ['InsideNonExistentFolder'] []
/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/builtin_modules/NonExistentFolder/InsideNonExistentFolder [] []

python_seekho_scripts = os.path.join(os.path.dirname((os.path.abspath(''))))
for dirpath, dirnames, filenames in os.walk(python_seekho_scripts):
    print(dirpath, dirnames, filenames)

/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts ['numpy', 'basics', 'advanced', 'oop', 'pandas', 'builtin_modules', 'plotting'] ['readme.txt']
/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/numpy [] ['readme.txt', 'stack_vs_concatenate.py', 'dimensions_axis.py', 'digitize.py']
/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/basics [] ['nested_functions.py', 'for_loops.py', 'installing_packages.py', 'conditional_statements.py', 'copying_lists.py', 'args_and_kwargs.py', 'readme.txt', 'exceptions.py', 'lists.py', 'while_loops.py', 'dictionaries.py', 'generators.py', 'NewFile.json', 'functions.py', 'iterator_vs_iterable.py', 'variables.py', 'operators.py', 'sets.py', 'io_operations.py', 'global_vs_local.py', 'sequential_data.py', 'NewFile', 'keywords.py', 'print_function.py']
/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/advanced [] ['reg_expressions.py', 'daily_q.csv', 'readme.txt', 'interfacing_with_fortran.py', 'parallel_processing.py', 'interfacing_with_c_cpp.py', 'unit_testing.py', 'read_csv_gpt.cpp', 'interfacing_with_matlab.py', 'interfacing_with_cpp.py', 'speeding_up_with_numba.py', 'scripts_to_executables.py', '_cython.py']
/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/oop [] ['class.py', '__getattr__.py', 'readme.txt', 'init.py', 'inheritance.py', 'call.py', 'class_vs_instance_attributes.py', 'attributes.py', 'str_repr.py', 'class_methods.py', 'introduction.py', 'public_vs_private_attributes.py', 'magical_methods.py', 'methods.py', 'static_methods.py', 'getattr_setattr.py', 'descriptors.py', 'property.py']
/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/pandas [] ['speeding_up.py', 'readme.txt', 'apply.py', 'pivot_vs_melt.py', 'multi-indexing.py', 'groupby.py', 'working_with_timeseries.py', 'dataframe_vs_series.py', 'io.py', 'indexing_vs_slicing.py']
/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/builtin_modules ['NonExistentFolder'] ['readme.txt', '_os.py', '_types_typing.py', '_csv.py', '_warnings.py', '_random_module.py', '_time.py', '_pathlib.py', '_sys.py', '_copy.py', '_collections.py', '_itertools.py', '_math.py']
/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/builtin_modules/NonExistentFolder ['InsideNonExistentFolder'] []
/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/builtin_modules/NonExistentFolder/InsideNonExistentFolder [] []
/home/docs/checkouts/readthedocs.org/user_builds/python-seekho/checkouts/dev/scripts/plotting [] ['_bar.py', 'readme.txt', '_plot.py', '_contour.py', 'marginal_plots.py', '_scatter.py', '_circular_bar.py', '_parallel_plot.py', 'intro.py', '_hist.py', '_dumbell.py', '_regplot.py', '_lollipop.py', '_ridge.py', '_boxplot.py', 'pie.py', '_taylor.py', '_violin.py', '_imshow.py', '_spider.py']

finding files

Let’s create few files first.

for i in range(5):
    with open(f'TextFile_{i}.txt', 'w'):
        pass
for i in range(5):
    with open(f'CsvFile_{i}.csv', 'w'):
        pass

If we want to find all files and folders within a specific path

path_to_look = os.getcwd()

print(os.listdir(path_to_look))

['NonExistentFolder', 'TextFile_1.txt', 'CsvFile_0.csv', 'readme.txt', 'TextFile_4.txt', '_os.py', 'CsvFile_4.csv', '_types_typing.py', 'CsvFile_1.csv', '_csv.py', 'CsvFile_2.csv', '_warnings.py', 'TextFile_2.txt', '_random_module.py', '_time.py', '_pathlib.py', '_sys.py', 'CsvFile_3.csv', 'TextFile_0.txt', '_copy.py', '_collections.py', '_itertools.py', '_math.py', 'TextFile_3.txt']

If we want to find only files and not folders/directories, we can do following list comprehension.

print([f for f in os.listdir(path_to_look) if os.path.isfile(f)])

['TextFile_1.txt', 'CsvFile_0.csv', 'readme.txt', 'TextFile_4.txt', '_os.py', 'CsvFile_4.csv', '_types_typing.py', 'CsvFile_1.csv', '_csv.py', 'CsvFile_2.csv', '_warnings.py', 'TextFile_2.txt', '_random_module.py', '_time.py', '_pathlib.py', '_sys.py', 'CsvFile_3.csv', 'TextFile_0.txt', '_copy.py', '_collections.py', '_itertools.py', '_math.py', 'TextFile_3.txt']

If we want to find files with a specific extension, we can do as following

print([f for f in os.listdir(path_to_look) if os.path.isfile(f) and f.endswith(".txt")])

['TextFile_1.txt', 'readme.txt', 'TextFile_4.txt', 'TextFile_2.txt', 'TextFile_0.txt', 'TextFile_3.txt']

If we want to find files with a specific extension, and starting with a specific name, we can do as following

print([f for f in os.listdir(path_to_look) if os.path.isfile(f) and f.endswith(".txt") and f.startswith('TextFile_')])

['TextFile_1.txt', 'TextFile_4.txt', 'TextFile_2.txt', 'TextFile_0.txt', 'TextFile_3.txt']

number of lessons in python-seekho book

scripts = [fname  for f in os.walk(python_seekho_scripts) for fname in f[2] if fname.endswith('.py')]
print(scripts)

['stack_vs_concatenate.py', 'dimensions_axis.py', 'digitize.py', 'nested_functions.py', 'for_loops.py', 'installing_packages.py', 'conditional_statements.py', 'copying_lists.py', 'args_and_kwargs.py', 'exceptions.py', 'lists.py', 'while_loops.py', 'dictionaries.py', 'generators.py', 'functions.py', 'iterator_vs_iterable.py', 'variables.py', 'operators.py', 'sets.py', 'io_operations.py', 'global_vs_local.py', 'sequential_data.py', 'keywords.py', 'print_function.py', 'reg_expressions.py', 'interfacing_with_fortran.py', 'parallel_processing.py', 'interfacing_with_c_cpp.py', 'unit_testing.py', 'interfacing_with_matlab.py', 'interfacing_with_cpp.py', 'speeding_up_with_numba.py', 'scripts_to_executables.py', '_cython.py', 'class.py', '__getattr__.py', 'init.py', 'inheritance.py', 'call.py', 'class_vs_instance_attributes.py', 'attributes.py', 'str_repr.py', 'class_methods.py', 'introduction.py', 'public_vs_private_attributes.py', 'magical_methods.py', 'methods.py', 'static_methods.py', 'getattr_setattr.py', 'descriptors.py', 'property.py', 'speeding_up.py', 'apply.py', 'pivot_vs_melt.py', 'multi-indexing.py', 'groupby.py', 'working_with_timeseries.py', 'dataframe_vs_series.py', 'io.py', 'indexing_vs_slicing.py', '_os.py', '_types_typing.py', '_csv.py', '_warnings.py', '_random_module.py', '_time.py', '_pathlib.py', '_sys.py', '_copy.py', '_collections.py', '_itertools.py', '_math.py', '_bar.py', '_plot.py', '_contour.py', 'marginal_plots.py', '_scatter.py', '_circular_bar.py', '_parallel_plot.py', 'intro.py', '_hist.py', '_dumbell.py', '_regplot.py', '_lollipop.py', '_ridge.py', '_boxplot.py', 'pie.py', '_taylor.py', '_violin.py', '_imshow.py', '_spider.py']

print(f"Total number of lessons in python-seekho book are {len(scripts)}.")

Total number of lessons in python-seekho book are 91.