PythonBasics: Difference between revisions
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=== Executing Scripts === | === Executing Scripts === | ||
The most basic way to execute a set of python commands (aside from just copying and pasting to the shell) is to use the '''execfile''' command. Calling '''execfile('myscript.py')''' from inside a python shell will execute 'myscript.py' one line at a time. You can use this to run a series of reduction commands or other simple scripts. | The most basic way to execute a set of python commands (aside from just copying and pasting to the shell) is to use the '''execfile''' command. Calling '''execfile('myscript.py')''' from inside a python shell will execute 'myscript.py' one line at a time. You can use this to run a series of reduction commands or other simple scripts. In fact, calling '''execfile''' on one or more scripts will almost certainly be sufficient to script most basic CASA data reductions. | ||
''A simple example'' | ''A simple example'' | ||
You can combine the control flow that we learned above with '''execfile''' to refine your scripts. For example, you might have a sophisticated reduction path that requires a few user inputs, which could be collected at the top of the script as variables. The reduction might have several discrete parts, which you could turn on or off using booleans and if statements. As an example, try creating a file that holds the following: | |||
''An example with a bit of control flow.'' | |||
As you edit the variables and booleans, various parts of the script will run tuned by the variables you set. This simple but powerful approach can (if you desire) form the infrastructure for a lot of your CASA reduction scripting. | |||
=== Functions === | === Functions === | ||
Revision as of 01:42, 10 October 2011
Simple Variables
Basic Math
Ints and Floats
Booleans
Deleting Variables
Checking Whether a Variable Exists
Data Collections: Lists
Lists are one of the fundamental data collections in python (we will also discuss dictionaries and you may want to read about tuples and sets).
Data Collections: Dictionaries
Dictionaries are another basic python data collection. Dictionaries store data in pairs, with a set of unique keys each mapped to some value (the values do not have to be unique). Dictionaries are extremely useful in scripting. For example, imagine that we are reducing a complex set of observations and want to be able to look up a the calibrator associated with a given source.
Control Flow
If
While
For
Break/Continue
More Complex Programs
Executing Scripts
The most basic way to execute a set of python commands (aside from just copying and pasting to the shell) is to use the execfile command. Calling execfile('myscript.py') from inside a python shell will execute 'myscript.py' one line at a time. You can use this to run a series of reduction commands or other simple scripts. In fact, calling execfile on one or more scripts will almost certainly be sufficient to script most basic CASA data reductions.
A simple example
You can combine the control flow that we learned above with execfile to refine your scripts. For example, you might have a sophisticated reduction path that requires a few user inputs, which could be collected at the top of the script as variables. The reduction might have several discrete parts, which you could turn on or off using booleans and if statements. As an example, try creating a file that holds the following:
An example with a bit of control flow.
As you edit the variables and booleans, various parts of the script will run tuned by the variables you set. This simple but powerful approach can (if you desire) form the infrastructure for a lot of your CASA reduction scripting.
Functions
Python allows you to define functions either from the command line (or an execfile call) or as part of modules.
