list comprehension while calling a function in python

Question

consider the following text in rhino python where arrPts is a list of points

start_point = rs.GetPoint()
arrPts0 = []
arrPts0 = rs.GetPoints()

arrPts=[]
for ind, pt in enumerate(arrPts0):
    arrPts.append( [pt,ind, 'angle','vector',0] )

then I run the arrPts through a function (def) which replaces 'angle' with actual strings of angles (e.g. '>45') and then I want to run through the following code which ends up calling another separate function (def) called 'add_Vectors':

Vectors = []
newPts = []
for pt in arrPts:
    if '>45' or '<45' in pt[2]:
        newPts.append(pt)

Vectors.append(add_Vectors(newPts, start_point))

how can I rewrite the above part with list comprehension so that it runs only when the condition is met instead of creating a new list (newPts) but working always on the main list (arrPts), if there's a function (def) in the way ?

something like:

Vectors.append(add_Vectors(newPts, start_point) ----> for '>45' in pt[2]

thanks

Pav

1h later...... tried this but doesn't seem to work:

newPts = []
Vectors = add_Vectors([newPts for pt in arrPts if '<45' in pt[2]], start_point)

Pav Ametvic · Accepted Answer · 2012-11-23 19:46:22Z

1

and I think I found the correct syntax for just 1 line !

Vectors = add_Vectors([pt for pt in arrPts if '<45' in pt[2]], start_point)

answered Nov 23, 2012 at 19:46

Pav Ametvic

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1 Comment

Marcin Over a year ago

If you switch from [] to () you'll have a generator expression, which won't have to generate the whole list before add_Vectors is called.

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