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Update standard library lesson
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@jarrodmillman
jarrodmillman committed Apr 9, 2024
1 parent cccd362 commit 5e8c7a7
Showing 1 changed file with 99 additions and 159 deletions.
258 changes: 99 additions & 159 deletions intro/language/standard_library.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -20,67 +20,59 @@ Current directory:

.. ipython::

In [17]: os.getcwd()
Out[17]: '/Users/cburns/src/scipy2009/scipy_2009_tutorial/source'
In [1]: import os

In [2]: os.getcwd()
Out[2]: '/home/jarrod/src/scientific-python-lectures/intro'

List a directory:

.. ipython::

In [31]: os.listdir(os.curdir)
Out[31]:
['.index.rst.swo',
'.python_language.rst.swp',
'.view_array.py.swp',
'_static',
'_templates',
'basic_types.rst',
'conf.py',
'control_flow.rst',
'debugging.rst',
...
In [3]: os.listdir(os.curdir)
Out[3]: ['intro.rst', 'scipy', 'language', 'matplotlib', 'index.rst', 'numpy', 'help']

Make a directory:

.. ipython::

In [32]: os.mkdir('junkdir')
In [4]: os.mkdir('junkdir')

In [33]: 'junkdir' in os.listdir(os.curdir)
Out[33]: True
In [5]: 'junkdir' in os.listdir(os.curdir)
Out[5]: True

Rename the directory:

.. ipython::

In [36]: os.rename('junkdir', 'foodir')
In [6]: os.rename('junkdir', 'foodir')

In [37]: 'junkdir' in os.listdir(os.curdir)
Out[37]: False
In [7]: 'junkdir' in os.listdir(os.curdir)
Out[7]: False

In [38]: 'foodir' in os.listdir(os.curdir)
Out[38]: True
In [8]: 'foodir' in os.listdir(os.curdir)
Out[8]: True

In [41]: os.rmdir('foodir')
In [9]: os.rmdir('foodir')

In [42]: 'foodir' in os.listdir(os.curdir)
Out[42]: False
In [10]: 'foodir' in os.listdir(os.curdir)
Out[10]: False

Delete a file:

.. ipython::

In [44]: fp = open('junk.txt', 'w')
In [11]: fp = open('junk.txt', 'w')

In [45]: fp.close()
In [12]: fp.close()

In [46]: 'junk.txt' in os.listdir(os.curdir)
Out[46]: True
In [13]: 'junk.txt' in os.listdir(os.curdir)
Out[13]: True

In [47]: os.remove('junk.txt')
In [14]: os.remove('junk.txt')

In [48]: 'junk.txt' in os.listdir(os.curdir)
Out[48]: False
In [15]: 'junk.txt' in os.listdir(os.curdir)
Out[15]: False

``os.path``: path manipulations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Expand All @@ -89,76 +81,50 @@ Delete a file:

.. ipython::

In [70]: fp = open('junk.txt', 'w')
In [16]: fp = open('junk.txt', 'w')

In [71]: fp.close()
In [17]: fp.close()

In [72]: a = os.path.abspath('junk.txt')
In [18]: a = os.path.abspath('junk.txt')

In [73]: a
Out[73]: '/Users/cburns/src/scipy2009/scipy_2009_tutorial/source/junk.txt'
In [19]: a
Out[19]: '/home/jarrod/src/scientific-python-lectures/intro/junk.txt'

In [74]: os.path.split(a)
Out[74]: ('/Users/cburns/src/scipy2009/scipy_2009_tutorial/source',
'junk.txt')
In [20]: os.path.split(a)
Out[20]: ('/home/jarrod/src/scientific-python-lectures/intro', 'junk.txt')

In [78]: os.path.dirname(a)
Out[78]: '/Users/cburns/src/scipy2009/scipy_2009_tutorial/source'
In [21]: os.path.dirname(a)
Out[21]: '/home/jarrod/src/scientific-python-lectures/intro'

In [79]: os.path.basename(a)
Out[79]: 'junk.txt'
In [22]: os.path.basename(a)
Out[22]: 'junk.txt'

In [80]: os.path.splitext(os.path.basename(a))
Out[80]: ('junk', '.txt')
In [23]: os.path.splitext(os.path.basename(a))
Out[23]: ('junk', '.txt')

In [84]: os.path.exists('junk.txt')
Out[84]: True
In [24]: os.path.exists('junk.txt')
Out[24]: True

In [86]: os.path.isfile('junk.txt')
Out[86]: True
In [25]: os.path.isfile('junk.txt')
Out[25]: True

In [87]: os.path.isdir('junk.txt')
Out[87]: False
In [26]: os.path.isdir('junk.txt')
Out[26]: False

In [88]: os.path.expanduser('~/local')
Out[88]: '/Users/cburns/local'
In [27]: os.path.expanduser('~/local')
Out[27]: '/home/jarrod/local'

In [92]: os.path.join(os.path.expanduser('~'), 'local', 'bin')
Out[92]: '/Users/cburns/local/bin'
In [28]: os.path.join(os.path.expanduser('~'), 'local', 'bin')
Out[28]: '/home/jarrod/local/bin'

Running an external command
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. ipython::

In [8]: os.system('ls')
basic_types.rst demo.py functions.rst python_language.rst standard_library.rst
control_flow.rst exceptions.rst io.rst python-logo.png
demo2.py first_steps.rst oop.rst reusing_code.rst

.. note:: Alternative to ``os.system``

A noteworthy alternative to ``os.system`` is the `sh module
<https://amoffat.github.com/sh/>`_. Which provides much more convenient ways to
obtain the output, error stream and exit code of the external command.

.. ipython::
:verbatim:

In [20]: import sh
In [20]: com = sh.ls()

In [21]: 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 [22]: print(com.exit_code)
0
In [23]: type(com)
Out[23]: sh.RunningCommand

In [29]: os.system('ls')
help index.rst intro.rst junk.txt language matplotlib numpy scipy
Out[29]: 0

Walking a directory
~~~~~~~~~~~~~~~~~~~~
Expand All @@ -167,16 +133,14 @@ Walking a directory

.. ipython::

In [10]: for dirpath, dirnames, filenames in os.walk(os.curdir):
....: for fp in filenames:
....: print(os.path.abspath(fp))
....:
....:
/Users/cburns/src/scipy2009/scipy_2009_tutorial/source/.index.rst.swo
/Users/cburns/src/scipy2009/scipy_2009_tutorial/source/.view_array.py.swp
/Users/cburns/src/scipy2009/scipy_2009_tutorial/source/basic_types.rst
/Users/cburns/src/scipy2009/scipy_2009_tutorial/source/conf.py
/Users/cburns/src/scipy2009/scipy_2009_tutorial/source/control_flow.rst
In [31]: for dirpath, dirnames, filenames in os.walk(os.curdir):
...: for fp in filenames:
...: print(os.path.abspath(fp))
...:
/home/jarrod/src/scientific-python-lectures/intro/intro.rst
/home/jarrod/src/scientific-python-lectures/intro/index.rst
/home/jarrod/src/scientific-python-lectures/intro/junk.txt
/home/jarrod/src/scientific-python-lectures/intro/index.rst
...

Environment variables:
Expand All @@ -185,35 +149,12 @@ Environment variables:
.. ipython::
:verbatim:

In [9]: import os

In [11]: os.environ.keys()
Out[11]:
['_',
'FSLDIR',
'TERM_PROGRAM_VERSION',
'FSLREMOTECALL',
'USER',
'HOME',
'PATH',
'PS1',
'SHELL',
'EDITOR',
'WORKON_HOME',
'PYTHONPATH',
...

In [12]: os.environ['PYTHONPATH']
Out[12]: '.:/Users/cburns/src/utils:/Users/cburns/src/nitools:
/Users/cburns/local/lib/python2.5/site-packages/:
/usr/local/lib/python2.5/site-packages/:
/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5'

In [16]: os.getenv('PYTHONPATH')
Out[16]: '.:/Users/cburns/src/utils:/Users/cburns/src/nitools:
/Users/cburns/local/lib/python2.5/site-packages/:
/usr/local/lib/python2.5/site-packages/:
/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5'
In [32]: os.environ.keys()
Out[32]: KeysView(environ({'SHELL': '/bin/bash', 'COLORTERM': 'truecolor', ...}))


In [34]: os.environ['SHELL']
Out[34]: '/bin/bash'


``shutil``: high-level file operations
Expand All @@ -234,12 +175,10 @@ Find all files ending in ``.txt``:

.. ipython::

In [18]: import glob

In [19]: glob.glob('*.txt')
Out[19]: ['holy_grail.txt', 'junk.txt', 'newfile.txt']
In [36]: import glob

In [37]: glob.glob('*.txt')
Out[37]: ['junk.txt']
``sys`` module: system-specific information
--------------------------------------------
Expand All @@ -248,41 +187,41 @@ System-specific information related to the Python interpreter.

* Which version of python are you running and where is it installed:

.. ipython::
.. ipython::

In [117]: sys.platform
Out[117]: 'darwin'

In [118]: sys.version
Out[118]: '2.5.2 (r252:60911, Feb 22 2008, 07:57:53) \n
[GCC 4.0.1 (Apple Computer, Inc. build 5363)]'
In [39]: import sys

In [119]: sys.prefix
Out[119]: '/Library/Frameworks/Python.framework/Versions/2.5'
In [40]: sys.platform
Out[40]: 'linux'

* List of command line arguments passed to a Python script:
In [41]: sys.version
Out[41]: '3.11.8 (main, Feb 28 2024, 00:00:00) [GCC 13.2.1 20231011 (Red Hat 13.2.1-4)]'

.. ipython::
In [42]: sys.prefix
Out[42]: '/home/jarrod/.venv/nx'

In [100]: sys.argv
Out[100]: ['/Users/cburns/local/bin/ipython']
* List of command line arguments passed to a Python script:

.. ipython::

In [43]: sys.argv
Out[43]: ['/home/jarrod/.venv/nx/bin/ipython']

``sys.path`` is a list of strings that specifies the search path for
modules. Initialized from PYTHONPATH:

.. ipython::

In [121]: sys.path
Out[121]:
['',
'/Users/cburns/local/bin',
'/Users/cburns/local/lib/python2.5/site-packages/grin-1.1-py2.5.egg',
'/Users/cburns/local/lib/python2.5/site-packages/argparse-0.8.0-py2.5.egg',
'/Users/cburns/local/lib/python2.5/site-packages/urwid-0.9.7.1-py2.5.egg',
'/Users/cburns/local/lib/python2.5/site-packages/yolk-0.4.1-py2.5.egg',
'/Users/cburns/local/lib/python2.5/site-packages/virtualenv-1.2-py2.5.egg',
...
In [44]: sys.path
Out[44]:
['/home/jarrod/.venv/nx/bin',
'/usr/lib64/python311.zip',
'/usr/lib64/python3.11',
'/usr/lib64/python3.11/lib-dynload',
'',
'/home/jarrod/.venv/nx/lib64/python3.11/site-packages',
'/home/jarrod/.venv/nx/lib/python3.11/site-packages']

``pickle``: easy persistence
-------------------------------
Expand All @@ -291,19 +230,20 @@ Useful to store arbitrary objects to a file. Not safe or fast!

.. ipython::

In [1]: import pickle
In [45]: import pickle

In [2]: l = [1, None, 'Stan']
In [46]: l = [1, None, 'Stan']

In [3]: with open('test.pkl', 'wb') as file:
...: pickle.dump(l, file)
...:
In [47]: with open('test.pkl', 'wb') as file:
...: pickle.dump(l, file)
...:

In [4]: with open('test.pkl', 'rb') as file:
...: out = pickle.load(file)
...:
In [48]: with open('test.pkl', 'rb') as file:
...: out = pickle.load(file)
...:

In [5]: out
In [49]: out
Out[49]: [1, None, 'Stan']


.. topic:: Exercise
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