Edit: see 
I encountered a problem getting Piston to work correctly that I have not seen discussed. I managed to figure out a fix myself, so I'm partially posting this because I feel like a genius and want to brag, but mostly in case anyone has the same problem and needs a reference.
When I installed piston, It worked fine except for one problem. I could not use the "addkey" function. Any time I tried, Piston would ask for my wallet password, and then hang indefinitely until I broke out with control-c. It produced this:
^CTraceback (most recent call last):
File "/home/sigmajin/.local/bin/piston", line 11, in <module>
sys.exit(main())
File "/home/sigmajin/.local/lib/python3.5/site-packages/piston/__main__.py", line 816, in main
pub = (steem.wallet.addPrivateKey(wifkey))
File "/home/sigmajin/.local/lib/python3.5/site-packages/piston/wallet.py", line 243, in addPrivateKey
self.keyStorage.add(self.encrypt_wif(wif), pub)
File "/home/sigmajin/.local/lib/python3.5/site-packages/piston/wallet.py", line 187, in encrypt_wif
return format(bip38.encrypt(PrivateKey(wif), self.masterpassword), "encwif")
File "/home/sigmajin/.local/lib/python3.5/site-packages/graphenebase/bip38.py", line 61, in encrypt
key = scrypt.scrypt(bytes(passphrase, "utf-8"), salt, 16384, 8, 8)
File "/home/sigmajin/.local/lib/python3.5/site-packages/pylibscrypt/pypyscrypt_inline.py", line 212, in scrypt
smix(B, i * 32 * r, r, N, V, XY)
File "/home/sigmajin/.local/lib/python3.5/site-packages/pylibscrypt/pypyscrypt_inline.py", line 175, in smix
blockmix_salsa8(X, 32 * r, r) # ROMix - 9(outer)
File "/home/sigmajin/.local/lib/python3.5/site-packages/pylibscrypt/pypyscrypt_inline.py", line 155, in blockmix_salsa8
salsa20_8(X, tmp, BY, i * 16, BY, Yi + i*16) # BlockMix - 3(outer)
File "/home/sigmajin/.local/lib/python3.5/site-packages/pylibscrypt/pypyscrypt_inline.py", line 77, in salsa20_8
I'm don't know anything about programming, so obviously, I have no idea what any of this means, but I was able to find someone who had experienced a similar problem that produced a similar traceback with another program here:
https://github.com/cathalgarvey/deadlock/issues/4
The solution given for this program was to upgrade to the latest version, which included a fix. So I just installed the program (called deadlock), and it fixed my issue . I'm sure there is a better way to do it, but I wasn't really clear enough on the explanation to try and figure it out.
Hopefully, this post saves someone a little bit of time.
EDIT: though the above worked for me, the real and more direct fix (courtesy of
pip3 install scrypt