I have a string in python in this format:
The "" above is to show that it is a string. Now I want to parse this string until I hit the first '' (an empty element after col3 in above example) and form a list with elements before this. So based on the sample example above the list that I should get will be ['col1', 'col2', 'col3']. How can I do this in python?
Convert the string to a list and use list operations to slice the string at the empty string:
>>> s = "['col1', 'col2', 'col3','', 'row1', 'row2']"
>>> import ast
>>> L = ast.literal_eval(s)
>>> L
['col1', 'col2', 'col3', '', 'row1', 'row2']
>>> L.index('')
3
>>> L[:L.index('')]
['col1', 'col2', 'col3']
ast library. Seems useful.
ast.literal_eval is a safe form of eval that can evaluate a string containing a Python expression. It won't execute "del /s c:\*" for example.ast.literal_eval also converting them to set,tuple etc. ?
"{1,2,3}" and "(1,2,3)" would create a set and a tuple.import re
import numpy as np
l ="['col1', 'col2', 'col3','', 'row1', 'row2']"
pattern = r"'([A-Za-z0-9_\./\\-]*)'"
m = re.findall(pattern, l)
mn = np.array(m)
rslt = list(np.split(mn, np.where(mn==''))[0])
Output:
rslt
Out[75]: ['col1', 'col2', 'col3']
Explanation:
In [78]: pattern = r"'([A-Za-z0-9_\./\\-]*)'"
...: m = re.findall(pattern, l)
...:
In [79]: m
Out[79]: ['col1', 'col2', 'col3', '', 'row1', 'row2']
In [80]: mn = np.array(m)
In [81]: [list(x) for x in np.split(mn, np.where(mn==''))]
Out[81]: [['col1', 'col2', 'col3'], ['', 'row1', 'row2']]
numpy and re when ast.literal_eval is sufficient.re works for general cases of string parsing. While for you, in this particular case, ast is the most suitable indeed! I also learnt something new through your question! Thanks!I wish I could parse your string directly using json but when I do, I get this error:
>>> import json
>>> json.loads("['col1', 'col2', 'col3','', 'row1', 'row2']")
...
ValueError: No JSON object could be decoded
So, I first replaced the single quotes with double quotes:
>>> s = "['col1', 'col2', 'col3','', 'row1', 'row2']"
>>> m = json.loads(s.replace("'", '"'))
>>> m
[u'col1', u'col2', u'col3', u'', u'row1', u'row2']
# find first index of empty string and the splice the list
>>> m[:m.index('')]
[u'col1', u'col2', u'col3']
