How to extract multiple specific string lines from another string?

Question

I'm using a FEM software (Code_Aster) which is developed in Python, but its file extension is .comm. However, Python snippets can be inserted in .comm files.

I have a function which returns a very long string containing nodes, elements, elements group, and so on in the below form:

My goal is to add each row to a list/dictionary with its associate coordinates or nodes. For example:

dct_nodes = {
    'N5': [
        9.99999999998248E-03,
        0.00000000000000E+00,
        0.00000000000000E+00
    ]
}

dct_elems = {
    'M5': ['N1', 'N5'],
    'M85': ['N342', 'N224', 'N378']
}

I tried regex with re.split, re.search, and re.findall but I don't seem to be able to get what I need. This is what I've done so far.

node_list = list()

for item in ttt.split("\n"):
    if len(item) != 0: # there are some lines with zero len
        if item[0] == 'N':
            node_list.append(re.sub("\s+", ",", item.strip()))

The type(node_list[0]) returns string, whereas I would like to have a nested list, so I can grab node_list[0][0] and node_list[0][1] for data manipulation. How can I split this string on , so I can have access to, for examples, the coordinates. I hope anyone can help.

Please, avoid posting images of text. It is a better practice to transcribe them instead. — accdias
– accdias, Commented Apr 26, 2022 at 11:01

Meysam Majnooni · Accepted Answer · 2022-04-27 18:45:54Z

1

If there are no other lines starting with N or M, the below script does the job perfectly.

import re

ttt="""
%
COOR_3D
N1      0       0       0
N2      1       5       9
N3      2       6       10
N4      3       7       11
N5      4       8       12

FINSF
%
SEG2
M1      N1      N2
M2      N3      N4
FINSF
%
TRIA3
M3      N5      N6      N7
M4      N8      N9      N11
M5      N12     N13     N14"""


def finder(var,string):
    temp_dic = dict()
    for item in string.split("\n"):
        if len(item) != 0: # there are some lines with zero len
            temp = re.sub("\s+", ",", item.strip()).split(',')
            if item[0] == var:
                temp_dic[temp[0]] = [e for e in temp[1:]]
    return temp_dic

                
nodes = finder('N',ttt)
elems = finder('M',ttt)

Please also note that if you need to do arithmetic manipulations on the coordinates of the nodes, you have to cast them to float because they are string yet. You can probably use a tertiary operator to decide if e should be cast to a float or remains a string. I hope you find this answer useful.

answered Apr 27, 2022 at 18:45

Meysam Majnooni

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1 Comment

Raymond Over a year ago

Thank you very much! It did the job and saved me a lot of time.

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