Recover Yahoo password that's stored on my Mac
Actually, the password may not be stored on your Mac since most log in services use the password to generate a cryptographically strong (or at least significantly longer) string that acts as a "cookie" to authenticate your client to access the servers that hold your yahoo content.

Unless you used a different program than Keychain to store the original password itself, you have checked the primary source of saved passwords on OS X and might not be able to recover the original password.