Python cleanups

[practicalswift]

Python cleanups:

• Avoid reference to undefined name: stderr does not exist, sys.stderr does
• Use print(...) instead of undefined printf(...)
• Avoid redefinition of variable (tx) in list comprehension
• Remove unused variables and/or function calls
• Use sys.exit(...) instead of exit(...): exit(...) should not be used in programs

[jnewbery]

Looks good. utACK. One question inline and another general question:

In commit Use the variable name _ to show that we are intentionally ignoring a return value, why not just ignore the return value?

[jnewbery]

I can't see how using tx is an issue. Does this cause a linter warning?

[practicalswift]

Yes it does :-)

$ flake8 test/functional/p2p-compactblocks.py | grep redefine
test/functional/p2p-compactblocks.py:296:31: F812 list comprehension redefines 'tx' from line 276

Should I remove the commit 263686d from this PR?

[jnewbery]

actually, let's just swap this list comprehension for a for loop. We're using it for its side-effects, so a for loop is clearer.

[jtimon]

what about something more clear like throwaway_txid or something of the sort?

[jtimon]

fast review ACK

[practicalswift]

@jnewbery Good point! I've now changed from _ = f() to f() for calls that appear to have side effects. For calls that appear to have no side effects I've simply removed the calls.

@jnewbery @jtimon Could you take a look at the updated version and see if it looks correct? :-)

[practicalswift]

Added two commits :-)

[jnewbery]

no need for this to be a tuple. Just:

ver, cmd, _, atyp = recvall(self.conn, 4)

There are other examples in commit Use the variable name _ for unused return values. I won't comment on each of them.

[jnewbery]

prefer:

hashZ = self.nodes[1].generate(2)[-1]

since it conveys the meaning better: "give me the hash of the last block generated".

same for the two examples below

[jnewbery]

Perhaps change these to comments rather than erase them (for context).

[practicalswift]

Good point! Fixed!

[jnewbery]

No harm in leaving these as comments.

[practicalswift]

Good point! Updated but GitHub doesn't show the # NODE_GETUTXO = (1 << 1) below (in the comment view), so it appears as if it is not fixed :-)

[jnewbery]

I can imagine these methods potentially being useful at some point. I don't think there's any need to remove them.

[jnewbery]

Please leave this for now.

[jnewbery]

Mostly ACK, but a few comments.

[practicalswift]

@jnewbery Thanks for reviewing! Good feedback - I've addressed all points raised. Would you mind re-reviewing? :-)

[jnewbery]

Looks good. Just #10781 (comment) unaddressed (using a for loop instead of list comprehension for functions with side-effects)

[practicalswift]

@jnewbery Thanks! List comprehension now fixed as well. Looks good? :-)

[jnewbery]

looks good. utACK db442ad