How do I remove line breaks and only return characters between two substrings in a list?-CodePudding

If I have a string like:

query = """
SELECT
   alias.column_one,
   alias.column_two,
   alias.column_three
FROM
   table_name
"""

How do I just return the characters between "SELECT" and "FROM" in a list so I have a list like below which also accounts for line breaks:

columns = ['alias.column_one', 'alias.column_two', 'alias.column_three']

I've tried importing re but I'm still stuck

CodePudding user response：

You could try this:

query = """
SELECT
   alias.column_one,
   alias.column_two,
   alias.column_three
FROM
   table_name
"""

columns = query.split('\n') # split the string at every line break - '\n'
columns = [column.strip() for column in columns] # strip out the leading spaces

# take the slice of the list between 'SELECT' and 'FROM':
columns = columns[columns.index('SELECT') 1:columns.index('FROM')]

columns.index('SELECT') returns the index of the list columns at which the word 'SELECT' appears. columns.index('FROM') does the same thing for 'FROM'. By taking a slice of columns between the first index (plus 1 - because the slice returns the value AT the first index) and the second index, you get only those elements between 'SELECT' and 'FROM'.

CodePudding user response：

You basically need the substring between 'SELECT' and 'FROM'. You could try something like this:

>>> s
'\nSELECT\n   alias.column_one,\n   alias.column_two,\n   
alias.column_three\nFROM\n   table_name\n'

>>> print((s.split('SELECT'))[1].split('FROM')[0])

alias.column_one,
alias.column_two,
alias.column_three

Since the question mentioned to get characters. Considering you wanted the result as a list, you could extend the above as:

>>> t = (s.split('SELECT'))[1].split('FROM')[0]
>>> [x.strip() for x in t.split(',\n')]
['alias.column_one', 'alias.column_two', 'alias.column_three']

CodePudding user response：

use re to get the string between SELECT and FROM, in this case is

   alias.column_one,
   alias.column_two,
   alias.column_three

then split the string by ',' and use strip() method to remove blank characters at the beginning and end

import re

query = """
SELECT
   alias.column_one,
   alias.column_two,
   alias.column_three
FROM
   table_name
"""

pattern = re.compile(r'SELECT(?P<column>[\S\s] ?)FROM')
result = pattern.search(query)
columns = result.group('column').split(',')
columns = list(map(lambda x:x.strip(),columns))
print(columns)