Pattern Matching Over Python Lists

[Chris]

Is anyone aware of any prior work done with searching or matching a
pattern over nested Python lists? I have this problem where I have a
list like:

[1, 2, [1, 2, [1, 7], 9, 9], 10]

and I'd like to search for the pattern [1, 2, ANY] so that is returns:

[1, 2, [1, 2, [6, 7], 9, 9], 10]
[1, 2, [6, 7], 9, 9]

 

[bearophileHUGS]

Kirk Strauser:

Hint: recursion. Your general algorithm will be something like:

Another solution is to use a better (different) language, that has
built-in pattern matching, or allows to create one.

Bye,
bearophile

 

[Chris]

Thanks for your help. Those weren't quite what I was looking for, but
I ended up figuring it out on my own. Turns out you can actually
search nested Python lists using simple regular expressions.

 

[Chris]

Kirk Strauser:


Another solution is to use a better (different) language, that has
built-in pattern matching, or allows to create one.

Bye,
bearophile

Btw, Python's stdlib includes a regular expression library. I'm not
sure if you're trolling or simply unaware of it, but I've found it
quite adequate for most tasks.

 

[John Machin]

Btw, Python's stdlib includes a regular expression library. I'm not
sure if you're trolling or simply unaware of it, but I've found it
quite adequate for most tasks.

Kindly consider a third possibility: bearophile is an experienced
Python user, has not to my knowledge exhibited any troll-like
behaviour in the past, and given that you seem to be happy using the
re module not on strings but on lists of integers, may have been
wondering whether *you* were trolling or just plain confused but just
too polite to wonder out loud

 

[Paddy]

Thanks for your help. Those weren't quite what I was looking for, but
I ended up figuring it out on my own. Turns out you can actually
search nested Python lists using simple regular expressions.

Strange?
How do you match nested '[' ... ']' brackets?

- Paddy.

 

[MRAB]

Btw, Python's stdlib includes a regular expression library. I'm not
sure if you're trolling or simply unaware of it, but I've found it
quite adequate for most tasks.

bearophile was talking about matching lists and tuples, not matching
strings.

Python's regular expression module works with characters in strings,
but the same approach can be applied to items in lists and tuples.

 

[Chris]

Kindly consider a third possibility: bearophile is an experienced
Python user, has not to my knowledge exhibited any troll-like
behaviour in the past, and given that you seem to be happy using the
re module not on strings but on lists of integers, may have been
wondering whether *you* were trolling or just plain confused but just
too polite to wonder out loud

Fair enough. To help you understand the method I used, I'll give you
this hint. It's true that regex on works on strings. However, is there
any way to convert arbitrarily complex data structures to string
representations? You don't need to be an experienced Python user to
answer to this

 

[eliben]

Fair enough. To help you understand the method I used, I'll give you

this hint. It's true that regex on works on strings. However, is there
any way to convert arbitrarily complex data structures to string
representations? You don't need to be an experienced Python user to
answer to this

As Paddy noted before, your solution has a problem, Regexes can't
match nested parenthesis, so I think your method will have a problem
with nested lists, unless your actual inputs are much simpler than the
general case.

Eli