matching python multiline expression string from a file using grep?

With GNU grep

$ grep -zoE "'depends'"':\s*\[[^][]+]' ip.txt | tr '\0' '\n'
'depends': [
        'base_setup', 
        'membership',
        'event'
    ]

• -z option will cause grep to use ASCII NUL character as separator. So, assuming your input file doesn't have this character, effectively this means the input is read as a single string
• -o to get only matching portion
• "'depends'"':\s*\[[^][]+]' will match 'depends': followed by optional whitespaces followed by [ character followed by one or more non [] characters followed by ]
  • this means any nested [] sequences won't be suited for this solution
• tr '\0' '\n' to convert NUL character to newline, as -z will also mean NUL as separator in the output

With ripgrep:

$ rg -oUN "'depends'"':\s*\[[^\]\[]+]' ip.txt
'depends': [
        'base_setup', 
        'membership',
        'event'
    ]

The advantage is that this doesn't depend upon NUL character and doesn't have to read entire input in one go. -U is multiline matching option and -N turns off line number prefix (which is on by default for terminal output). Also, both GNU grep and rg support recursive searching.

If your data to be matched is always whole lines, with 'depends': [ in a single line, you could also use awk. See How to print lines between two patterns, inclusive or exclusive (in sed, AWK or Perl)? for explanations.

$ awk '/\047depends\047:[[:blank:]]*\[/{f=1} f; /]/{f=0}' ip.txt
    'depends': [
        'base_setup', 
        'membership',
        'event'
    ],