Python/Miscellaneous Snippets and Tips - Revision history

Jrwrigh: Remove paraview and post-processing categories

2022-09-18T17:13:22Z

Remove paraview and post-processing categories

Jrwrigh: Add python category

2022-09-18T17:12:38Z

Add python category

Jrwrigh: Add module reloading info

2022-09-18T17:08:03Z

Add module reloading info

Jrwrigh: Finish nested Python objects and operator precedence

2021-09-07T15:27:07Z

Finish nested Python objects and operator precedence

Jrwrigh: /* Nested Python Objects and Operator Precedence */

2021-09-07T15:01:17Z

‎Nested Python Objects and Operator Precedence

Jrwrigh: Start operator precedence section

2021-09-07T15:00:25Z

Start operator precedence section

Jrwrigh: /* [...] vs (...) */

2021-09-07T14:53:19Z

‎[...] vs (...)

Jrwrigh: /* [...] vs (...) */ Add examples of getting values from objects

2021-09-06T18:35:34Z

‎[...] vs (...): Add examples of getting values from objects

Jrwrigh: Add Matlab migration section

2021-08-10T15:27:25Z

Add Matlab migration section

Jrwrigh: /* Unix Shebang */

2021-08-10T14:58:05Z

‎Unix Shebang

@@ Line 107: / Line 107: @@
 Note we do not need to invoke <code>np.column_stack</code>, and thus we don't spend time copying data or take up memory with redundant data.
-== Running Python Files in Terminal ==[[Category:Paraview]]  [[Category:Post-processing]]
+== Running Python Files in Terminal ==
 There are a few ways to run Python files (and Python code more generally): via a Unix shebang, <code>python</code>, inside a <code>ipython</code> instance, or through an IDE like <code>spyder</code>. We'll go over how to run a script, <code>script.py</code>, in the terminal:

@@ Line 107: / Line 107: @@
 Note we do not need to invoke <code>np.column_stack</code>, and thus we don't spend time copying data or take up memory with redundant data.
-== Running Python Files in Terminal ==
+== Running Python Files in Terminal ==[[Category:Paraview]]  [[Category:Post-processing]]
 There are a few ways to run Python files (and Python code more generally): via a Unix shebang, <code>python</code>, inside a <code>ipython</code> instance, or through an IDE like <code>spyder</code>. We'll go over how to run a script, <code>script.py</code>, in the terminal:
@@ Line 224: / Line 225: @@
           if type(attribute) is ModuleType:
               rreload(attribute)

← Older revision		Revision as of 17:08, 18 September 2022
Line 171:		Line 171:

	However Python's built-in console does not have the nice features of IPython, so it is generally preferred.		However Python's built-in console does not have the nice features of IPython, so it is generally preferred.
		+
		+	== "Which module version did I load?" and Reloading modules ==
		+
		+	When working with [[Vtkpytools]] and other in-development Python libraries, you may need to determine what version of the library you're working with, and may need to reload that library to get recently-added features.
		+
		+	The following examples will use [[Vtkpytools]] as the module in question. (with the preliminary that the library has been aliased via <code>import vtkpytools as vpt</code>).
		+
		+	=== Which module version did I load? ===
		+	You can check the release version via:
		+
		+	print(vpt.__version__)
		+	''Note, if you checking the <code>vtk</code> python library, you need to use <code>vtk.VTK_VERSION</code>, because vtk is special''
		+
		+	If you're dealing with development version of the library, the version information may not be updated. You can determine the '''path''' that the library was loaded from via:
		+
		+	print(vpt.__file__)
		+
		+	=== Reload the module ===
		+
		+	Note any new instance of a Python interpreter will automatically load a new version of a library; it is not cached outside of a single interpreter instance.
		+
		+	==== In IPython Console ====
		+	If you're using the IPython console (either [[#IPython_Console\|from commandline]], or from Spyder), you can use <code>dreload</code>:
		+
		+	dreload(vpt)
		+
		+	==== In Spyder ====
		+	If you're in Spyder, in addition to using <code>dreload</code> (specified above), rerunning a script will automatically reload any imported libraries. A message should appear in the console window saying which modules it reloaded.
		+
		+	==== Using Python standard library ====
		+	If either of the above is not working, or not a desirable solution, you can try to reload the module using the standard Python library:
		+
		+	from importlib import reload
		+	reload(vpt)
		+
		+	Note that this is a bit finicky, as only the top-level module is reloaded. So in this case, any changes made to the <code>vpt.barfiletools</code> module are ''not'' reloaded. Thus you have to do a recursive dance to reload everything. This can be better automated using [https://stackoverflow.com/a/17194836/7564988 this StackOverflow answer] (reprinted below):
		+
		+	from types import ModuleType
		+
		+	try:
		+	from importlib import reload # Python 3.4+
		+	except ImportError:
		+	# Needed for Python 3.0-3.3; harmless in Python 2.7 where imp.reload is just an
		+	# alias for the builtin reload.
		+	from imp import reload
		+
		+	def rreload(module):
		+	"""Recursively reload modules."""
		+	reload(module)
		+	for attribute_name in dir(module):
		+	attribute = getattr(module, attribute_name)
		+	if type(attribute) is ModuleType:
		+	rreload(attribute)

@@ Line 20: / Line 20: @@
 In general:
 * <code>[...]</code> gets a value from a Python object
-** Either by [https://docs.python.org/3/reference/expressions.html#subscriptions subscription] (<code>object[0]</code> or <code>object['asdf']</code>) or [https://docs.python.org/3/reference/expressions.html#slicings slicing] (<code>object[1:3]</code>)
+** Either by [https://docs.python.org/3/reference/expressions.html#subscriptions ''subscription''] (<code>object[0]</code> or <code>object['asdf']</code>) or [https://docs.python.org/3/reference/expressions.html#slicings ''slicing''] (<code>object[1:3]</code>)
 * <code>(...)</code> declares arguments to a function (like <code>range(3)</code>).
@@ Line 31: / Line 31: @@
   >>> lista[1:]   # Accessing all items of index 1 or greater
   ['b', 3]
-−
-  >>> lista[0] = (1, 3, 'asdf')   # Assigning a tuple to the 0th element
+  >>> dicta = {'a': 2, 'b':'foo'}
-  >>> lista
+  >>> dicta['a']   # Accessing the value of the key 'a'
- [(1, 3, 'asdf'), 'b', 3]
   >>> lista[0]    # Accessing the 0th item (the tuple)
@@ Line 43: / Line 69: @@
   >>> dicta = {'a': 2, 'b':'foo', 'bar':{'sub':'phasta'}}
-  >>> dicta['a']   # Accessing the value of the key 'a'
   >>> dicta['bar']  # Accessing the value of 'bar', a nested dictionary
   {'sub': 'phasta'}
   >>> dicta['bar']['sub'] # Accessing nested dictionary items
   'phasta'
 == Write Data to Text File (ie. CSV) ==

@@ Line 51: / Line 51: @@
 == Nested Python Objects and Operator Precedence ==
-Python allows you to "chain" "operations" together, somewhat similarly to piping in a POSIX Shell (ie. <code>ls | grep file</code>). If you see something like <code>object.data['foo'](arg)[:,2:4]</code>, this is just successive
+Python allows you to "chain" "operations" together, somewhat similarly to piping in a POSIX Shell (ie. <code>ls | grep file</code>). If you see something like <code>object.data['foo'](arg)[:,2:4]</code>, this is just successive operators chained together.
 == Write Data to Text File (ie. CSV) ==

@@ Line 15: / Line 15: @@
   [0, 1]
-==== <code>[...]</code> vs <code>(...)</code> ====
+==== <code>[...]</code> vs <code>(...)</code> after an object ====
 In general:
 * <code>[...]</code> gets a value from a Python object
 * <code>(...)</code> declares arguments to a function (like <code>range(3)</code>).
 '''Examples of getting a value from a Python object:'''

@@ Line 16: / Line 16: @@
 ==== <code>[...]</code> vs <code>(...)</code> ====
-Getting a value from a Python object is done using <code>[...]</code>. <code>(...)</code> is used almost exclusively for declaring arguments to a function (like <code>range(3)</code>).
+In general:
-The primary exception to this are when declaring tuples, which are simply immutable (not changeable) list objects in Python:
+The primary exception to this are when declaring [https://docs.python.org/3/library/stdtypes.html?highlight=tuples#tuple tuples] (immutable (not changeable) lists) and [https://docs.python.org/3/reference/expressions.html#generator-expressions generator expressions] (advanced shorthand for defining generator objects).
-  >>> test = (0, 1)
-  >>> test[0]
+'''Examples of getting a value from a Python object:'''
-−
-  >>> test[0] = 3
+  >>> lista = ['a', 'b', 3]
-  Traceback (most recent call last):
+ >>> lista[0]    # Accessing item 0
-    File "<stdin>", line 1, in <module>
+ 'a'
-  TypeError: 'tuple' object does not support item assignment
 == Write Data to Text File (ie. CSV) ==

← Older revision		Revision as of 15:27, 10 August 2021
Line 1:		Line 1:
	Here are miscellaneous tips and tricks when working with Python files.		Here are miscellaneous tips and tricks when working with Python files.
		+
		+	== Migrating from MATLAB ==
		+	Numpy (the defacto numerical array library in Python) has a handy [https://numpy.org/doc/stable/user/numpy-for-matlab-users.html guide for migrating from MATLAB to Numpy].
		+
		+	Here are some tips for general Python:
		+
		+	=== Indexing ===
		+	==== Python indices start with 0 instead of 1 ====
		+	This has several cascading effects in the language, such as:
		+	>>> test = list(range(3))
		+	>>> print(test) # Doesn't include 3, but creates 3 integers
		+	[0, 1, 2]
		+	>>> test[0:2] # Excludes the last index, so only 2 integers are returned
		+	[0, 1]
		+
		+	==== <code>[...]</code> vs <code>(...)</code> ====
		+	Getting a value from a Python object is done using <code>[...]</code>. <code>(...)</code> is used almost exclusively for declaring arguments to a function (like <code>range(3)</code>).
		+
		+	The primary exception to this are when declaring tuples, which are simply immutable (not changeable) list objects in Python:
		+	>>> test = (0, 1)
		+	>>> test[0]
		+	0
		+	>>> test[0] = 3
		+	Traceback (most recent call last):
		+	File "<stdin>", line 1, in <module>
		+	TypeError: 'tuple' object does not support item assignment

	== Write Data to Text File (ie. CSV) ==		== Write Data to Text File (ie. CSV) ==

@@ Line 41: / Line 41: @@
 ''Note: I'll be assuming usage of Python 3.X. If using Python 2.7, use <code>python</code> instead of <code>python3</code>''
 === Unix Shebang ===
-You can use a [https://en.wikipedia.org/wiki/Shebang_(Unix) Unix shebang] as the first line in a script. Then you can execute the script directly in a Linux terminal (if it has the appropriate execute permissions).
+Using a [https://en.wikipedia.org/wiki/Shebang_(Unix) Unix shebang], you can execute the script directly in a Linux terminal (if it has the appropriate execute permissions).
 This is done by adding a <code>#!/usr/bin/env python3</code> to the top of the file.
 This line is not read by Python (<code>#</code> is the comment character), but instead by the (Linux) kernel which uses the executable specified in the line to execute the file.