Scripts in Python

Python is the third language of the Script workspace. Choose Python in the language box above the editor (a .py file opens in Python by itself). Python, Lua and CraftScript share the same variables and the same built-in functions, so a Python script can use what a CraftScript script made, and the other way round.

The first Python run in a visit loads Python itself (about 13 MB) from this site, which takes a few seconds. Python is not part of Save for offline yet: run one Python script while online first.

Run only Python scripts you trust

The essentials

A = cs.magic(3)              # every built-in function is cs.<name>
B = A @ A.T                  # @ is the matrix product, .T the transpose
C = A * 2 + 1                # + - * / ** are elementwise, as in numpy
print(A[0, 1], A[-1, -1])    # 0-based; negative counts from the end
row = A[1]                   # one index on a matrix: a row
big = A[A > 4]               # a logical mask picks elements
A[0, 0] = -5                 # assigning into an array
V, D = cs.call('eig', 2, A)  # several results: cs.call(name, how many, …)

• A 1 × 1 array arrives as a plain number; other arrays, sparse matrices, meshes, fields and models are Values.
• A Value has shape (a tuple), T, type, numel(), copy(), tolist(), len() (its rows), and float(), int() and bool() for a single element.
• Comparisons (<, ==, …) are elementwise, as in numpy: they give a logical Value.
• Lists of numbers passed to a built-in function become arrays: cs.sum([1, 2, 3]). cs.tensor([[1, 2], [3, 4]]) makes a matrix.
• A dict becomes a struct and a list of mixed things a cell, and back again.

Every global your script makes (a number, a Value, a dict, a list…) lands in the Variables tab when the run ends, even after an error. Names starting with _, functions, classes and modules stay in Python. ws.name reads or sets a variable directly, and ws_names() lists them.

print(…) writes to the console. display(…) (or cs.display) shows a mesh, a field or a plot, as in CraftScript.

Call the analysis library

Library functions are called like built-in ones: cs.box_mesh(20, 10, 10, 5, 'hex'), cs.call('modal_tet', 2, …). Write the name in the script as it is: PartCraft finds the library functions a script uses before it runs.

Not there yet

• numpy, scipy and other packages: only Python's own standard library (math, json, itertools…) is here.
• Folding in the editor, and calling a Python function from a CraftScript script.
• A run checks the instruction budget and Stop every 1000 lines; a long calculation inside one built-in function finishes first.