1.2.7. Standard Library¶
Note
Reference document for this section:
The Python Standard Library documentation: https://docs.python.org/3/library/index.html
Python Essential Reference, David Beazley, Addison-Wesley Professional
1.2.7.1. os module: operating system functionality¶
“A portable way of using operating system dependent functionality.”
Directory and file manipulation¶
Current directory:
In [1]: import os
In [2]: os.getcwd()
Out[2]: '/tmp'
List a directory:
In [3]: os.listdir(os.curdir)
Out[3]:
['profile_fipa_q3s',
'profile_zpw1zshu',
'profile_yx2v9j1u',
'profile_hvadjvo0',
'profile_vjnmbn9t',
'profile_3e7b7mnh',
'profile_u_dkva9k',
'profile_1_ho6wsw',
'profile_17z9xbiu',
'profile_nhsyjqfm',
'profile_uyk_j767',
'profile_g6ucuiy9',
'profile_4anwydli',
'profile_wej8tpc7',
'dotnet-diagnostic-831-1101-socket',
'profile_x_2rv34s',
'profile_nnfonejt',
'clr-debug-pipe-831-1101-out',
'profile_h8ahy7fq',
'profile_hebci4u3',
'profile_662qdwyj',
'systemd-private-5a1e73d7020f41aebb5ccae2a9ef7f53-chrony.service-aXXAhc',
'profile_odcbc8pq',
'profile_rkxkqy6r',
'clr-debug-pipe-1824-12120-out',
'profile_un100jp7',
'profile_805ffpez',
'profile_ov3bujrd',
'profile_glp4r62l',
'systemd-private-5a1e73d7020f41aebb5ccae2a9ef7f53-polkit.service-kkpwfH',
'profile_5vwjni03',
'profile_buspmxtb',
'.ICE-unix',
'clr-debug-pipe-1824-12120-in',
'clr-debug-pipe-831-1101-in',
'systemd-private-5a1e73d7020f41aebb5ccae2a9ef7f53-ModemManager.service-Empwlt',
'snap-private-tmp',
'profile_sfdld8m4',
'systemd-private-5a1e73d7020f41aebb5ccae2a9ef7f53-systemd-logind.service-cYg7Es',
'profile_yc76tsby',
'profile_dcwdz0l1',
'profile_yho0ln7h',
'profile_99cs1dgd',
'systemd-private-5a1e73d7020f41aebb5ccae2a9ef7f53-systemd-resolved.service-nnkqv9',
'profile_a3cfjro5',
'profile_xxx9__92',
'profile_1e7iroyb',
'profile_dj6lnbhy',
'clr-debug-pipe-1808-11921-in',
'profile_0p2hwy1o',
'profile_md53_vd8',
'profile_u0zph5is',
'profile_lci7bgu5',
'dotnet-diagnostic-1824-12120-socket',
'profile_fo__gd4r',
'profile_c547dl1i',
'profile_oxmjht_b',
'profile_8j1j5lyh',
'profile_e07ps17i',
'profile_bklgzk93',
'profile_ypn7g29s',
'.XIM-unix',
'profile_ebl3yo6f',
'.X11-unix',
'profile_ajv63h_v',
'profile_hh8uhz1r',
'hsperfdata_root',
'profile_mn8s6x17',
'dotnet-diagnostic-1808-11921-socket',
'profile_7h7xd5mi',
'profile_3ckq9d03',
'profile_x8bqc_g8',
'profile_c57e_94a',
'profile_b49of1_b',
'clr-debug-pipe-1808-11921-out',
'profile_iohwvmzf',
'profile_gz7tsu91',
'profile_6f04cas7',
'profile_daahkszg',
'profile_ogv3klaq',
'profile_y0hi0gcb',
'profile_0j7pkhjb',
'profile_yyac79ne',
'systemd-private-5a1e73d7020f41aebb5ccae2a9ef7f53-haveged.service-KLck1c',
'.font-unix',
'profile_lu41b8dd',
'profile_1t3sdp4r',
'profile_hbu89y3v',
'profile_wmjz7lc4',
'profile_05dtmzwl',
'profile_8qxt95v9']
Make a directory:
In [4]: os.mkdir('junkdir')
In [5]: 'junkdir' in os.listdir(os.curdir)
Out[5]: True
Rename the directory:
In [6]: os.rename('junkdir', 'foodir')
In [7]: 'junkdir' in os.listdir(os.curdir)
Out[7]: False
In [8]: 'foodir' in os.listdir(os.curdir)
Out[8]: True
In [9]: os.rmdir('foodir')
In [10]: 'foodir' in os.listdir(os.curdir)
Out[10]: False
Delete a file:
In [11]: fp = open('junk.txt', 'w')
In [12]: fp.close()
In [13]: 'junk.txt' in os.listdir(os.curdir)
Out[13]: True
In [14]: os.remove('junk.txt')
In [15]: 'junk.txt' in os.listdir(os.curdir)
Out[15]: False
os.path: path manipulations¶
os.path provides common operations on pathnames.
In [16]: fp = open('junk.txt', 'w')
In [17]: fp.close()
In [18]: a = os.path.abspath('junk.txt')
In [19]: a
Out[19]: '/tmp/junk.txt'
In [20]: os.path.split(a)
Out[20]: ('/tmp', 'junk.txt')
In [21]: os.path.dirname(a)
Out[21]: '/tmp'
In [22]: os.path.basename(a)
Out[22]: 'junk.txt'
In [23]: os.path.splitext(os.path.basename(a))
Out[23]: ('junk', '.txt')
In [24]: os.path.exists('junk.txt')
Out[24]: True
In [25]: os.path.isfile('junk.txt')
Out[25]: True
In [26]: os.path.isdir('junk.txt')
Out[26]: False
In [27]: os.path.expanduser('~/local')
Out[27]: '/home/runner/local'
In [28]: os.path.join(os.path.expanduser('~'), 'local', 'bin')
Out[28]: '/home/runner/local/bin'
Running an external command¶
In [29]: os.system('ls')
Out[29]: 0
Note
Alternative to os.system
A noteworthy alternative to os.system is the sh module. Which provides much more convenient ways to
obtain the output, error stream and exit code of the external command.
In [30]: import sh
In [31]: com = sh.ls()
In [31]: print(com)
basic_types.rst exceptions.rst oop.rst standard_library.rst
control_flow.rst first_steps.rst python_language.rst
demo2.py functions.rst python-logo.png
demo.py io.rst reusing_code.rst
In [32]: type(com)
Out[32]: str
Walking a directory¶
os.path.walk generates a list of filenames in a directory tree.
In [33]: for dirpath, dirnames, filenames in os.walk(os.curdir):
....: for fp in filenames:
....: print(os.path.abspath(fp))
....:
....:
/tmp/dotnet-diagnostic-831-1101-socket
/tmp/clr-debug-pipe-831-1101-out
/tmp/clr-debug-pipe-1824-12120-out
/tmp/clr-debug-pipe-1824-12120-in
/tmp/clr-debug-pipe-831-1101-in
/tmp/junk.txt
/tmp/clr-debug-pipe-1808-11921-in
/tmp/dotnet-diagnostic-1824-12120-socket
/tmp/dotnet-diagnostic-1808-11921-socket
/tmp/clr-debug-pipe-1808-11921-out
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/dhist
/tmp/bookmarks
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
/tmp/README
Environment variables:¶
In [34]: os.environ.keys()
Out[34]: KeysView(environ({'SHELL': '/bin/bash', 'COLORTERM': 'truecolor', ...}))
In [35]: os.environ['SHELL']
Out[35]: '/bin/bash'
1.2.7.2. shutil: high-level file operations¶
The shutil provides useful file operations:
shutil.rmtree: Recursively delete a directory tree.
shutil.move: Recursively move a file or directory to another location.
shutil.copy: Copy files or directories.
1.2.7.3. glob: Pattern matching on files¶
The glob module provides convenient file pattern matching.
Find all files ending in .txt:
In [36]: import glob
In [37]: glob.glob('*.txt')
Out[37]: ['junk.txt']
1.2.7.4. sys module: system-specific information¶
System-specific information related to the Python interpreter.
Which version of python are you running and where is it installed:
In [38]: import sys
In [39]: sys.platform
Out[39]: 'linux'
In [40]: sys.version
Out[40]: '3.12.11 (main, Jun 4 2025, 04:14:08) [GCC 13.3.0]'
In [41]: sys.prefix
Out[41]: '/opt/hostedtoolcache/Python/3.12.11/x64'
List of command line arguments passed to a Python script:
In [42]: sys.argv
Out[42]:
['/opt/hostedtoolcache/Python/3.12.11/x64/lib/python3.12/site-packages/sphinx/__main__.py',
'-b',
'latex',
'-d',
'build/doctrees',
'.',
'build/latex']
sys.path is a list of strings that specifies the search path for
modules. Initialized from PYTHONPATH:
In [43]: sys.path
Out[43]:
['/home/runner/work/scientific-python-lectures/scientific-python-lectures',
'/opt/hostedtoolcache/Python/3.12.11/x64/lib/python312.zip',
'/opt/hostedtoolcache/Python/3.12.11/x64/lib/python3.12',
'/opt/hostedtoolcache/Python/3.12.11/x64/lib/python3.12/lib-dynload',
'/opt/hostedtoolcache/Python/3.12.11/x64/lib/python3.12/site-packages']
1.2.7.5. pickle: easy persistence¶
Useful to store arbitrary objects to a file. Not safe or fast!
In [44]: import pickle
In [45]: l = [1, None, 'Stan']
In [46]: with open('test.pkl', 'wb') as file:
....: pickle.dump(l, file)
....:
In [47]: with open('test.pkl', 'rb') as file:
....: out = pickle.load(file)
....:
In [48]: out
Out[48]: [1, None, 'Stan']