Utilities for Contract ABIs

[reedsa]

What was wrong?

Contract ABI utilities are useful for encoding and decoding contract transactions. Many utilities are implemented in web3.py as private methods.

Related to ethereum/web3.py#3036

These changes will be utilized in web3.py function/event utils:
ethereum/web3.py#3408
ethereum/web3.py#3401

How was it fixed?

Implements a public API for ABI utilities.

Todo:

• Clean up commit history

• Add or update documentation related to these changes

• Add entry to the release notes

Cute Animal Picture

[kclowes]

I like the new test functions, very nice! I didn't go through with a fine tooth comb, but looks good overall!

The only outstanding things I saw are:

• the comment around which exceptions to raise, and where they live
• I left a comment about raising vs returning an empty list. let me know what you think!

[pacrob]

Usage question - I pulled an ABI from web3 (extended_resolver.py), use get_all_function_abis to get function info, then take a name from that, say supportsInterface. From the description, I should be able to plug the abi and the function name into get_function_abi and get the same info back about that function, but I get:

MismatchedABI: 
Could not identify the intended function with name `supportsInterface`, positional arguments with type(s) `` and keyword arguments with type(s) `{}`.
Found 1 function(s) with the name `supportsInterface`: ['supportsInterface(bytes4)']
Function invocation failed due to improper number of arguments.

Same for get_function_info.

[fselmo]

It may look like a lot of comments but I left mostly nits, some things to discuss, and a few inconsistencies. The code looks great to me, most of it is around arg names, function names, deprecation cycle, and docstring blips.

[fselmo]

I think all my concerns were addressed here. Will wait to approve once the eth-typing branch / version gets decided and updated rather than using the git commit hash for the branch.