“Don’t let yesterday take up too much of today.” - Will Rogers

Case study

Assume you have a SQL INSERT statement like this:

INSERT INTO table_name VALUES (value1, value2, value3, ...);

If you want to split the values into a list, you can use the following code snippet:

import re
split_values = values.split(",")

If work in some case until for some values contains comma (,) inside single quotes (‘), like this:

INSERT INTO table_name VALUES (value1, value2, 'value3, value3.1', ...);

In this case, the split() method will not work as expected. To handle this case, you can use the following code snippet:

split_values = re.split(r",(?=(?:[^']*'[^']*')*[^']*$)", values)

Elaboration

Let’s break down the code snippet re.split(r",(?=(?:[^']*'[^']*')*[^']*$)", values):

The re.split() function is used to split a string based on a specified pattern. In this case, the pattern is ",(?=(?:[^']*'[^']*')*[^']*$)".

Now, let’s analyze the pattern:

  • , - This matches a comma (,) character, which serves as the delimiter for splitting the string.

  • (?=(?:[^’]’[^’]’)[^’]$) - This is a positive lookahead assertion. It ensures that the comma (,) is followed by a specific pattern without actually consuming it during the split.

  • (?:[^’]’[^’]’)* - This non-capturing group (?: … ) matches zero or more occurrences of the following pattern: any character except a single quote ([^’]), followed by a single quote (‘), followed by any character except a single quote ([^’]), and another single quote (‘). Essentially, it matches pairs of single quotes and any characters between them.

  • [^’]$ - This matches any character except a single quote ([^’]) until the end of the string ($). It ensures that there are no unmatched single quotes after the comma.

Therefore, the overall pattern ",(?=(?:[^']*'[^']*')*[^']*$)" matches a comma (,) only if it is followed by an even number of single quotes (indicating it is not inside a pair of quotes).

The re.split() function splits the values string based on this pattern, effectively separating the values for each column while ignoring commas inside quotes. The resulting list, split_values, contains the extracted values.

Note that the strip(“’”) method is applied to each value in the for loop to remove the surrounding single quotes.

–HTH–

Updated:

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