This is a part of a series and will work to build upon the last part. Part 1 is here. This post expects a very basic understanding of python syntax. This is going to introduce concepts of the steem-python library slowly at first to allow people to understand how to program their own stuff.

Source

Problem With Our Bot

from steem import Steem
from steem.post import Post

def loop():
    account = input("Enter Account: ")
    posting_key = input("Enter Key: ")
    s = Steem(keys=posting_key)
    while 1:
        link = input("Enter Link: ")
        link = link.replace(link[0:int(link.find('@'))],'')
        vw = float(input("Enter Voting Weight: "))
        pst = Post(link, s)
        pst.vote(vw, account)
        print('Voted!')


loop()

kryzsec@kryzsec-a101:~$ python manual_voter.py 
Enter Link: https://steemit.com/programming/@themarkymark/how-to-install-steem-python
Enter Voting Weight: 25
Traceback (most recent call last):
  File "manual_voter.py", line 17, in <module>
    loop()
  File "manual_voter.py", line 13, in loop
    pst.upvote(vw, account)
  File "/home/kryzsec/miniconda3/lib/python3.6/site-packages/steem/post.py", line 228, in upvote
    return self.vote(weight, voter=voter)
  File "/home/kryzsec/miniconda3/lib/python3.6/site-packages/steem/post.py", line 248, in vote
    return self.commit.vote(self.identifier, weight, account=voter)
  File "/home/kryzsec/miniconda3/lib/python3.6/site-packages/steem/commit.py", line 360, in vote
    return self.finalizeOp(op, account, "posting")
  File "/home/kryzsec/miniconda3/lib/python3.6/site-packages/steem/commit.py", line 128, in finalizeOp
    return tx.broadcast()
  File "/home/kryzsec/miniconda3/lib/python3.6/site-packages/steem/transactionbuilder.py", line 131, in broadcast
    raise e
  File "/home/kryzsec/miniconda3/lib/python3.6/site-packages/steem/transactionbuilder.py", line 129, in broadcast
    self.steemd.broadcast_transaction(self.json())
  File "/home/kryzsec/miniconda3/lib/python3.6/site-packages/steem/steemd.py", line 858, in broadcast_transaction
    return self.exec('broadcast_transaction', signed_transaction, api='network_broadcast_api')
  File "/home/kryzsec/miniconda3/lib/python3.6/site-packages/steembase/http_client.py", line 192, in exec
    return_with_args=return_with_args)
  File "/home/kryzsec/miniconda3/lib/python3.6/site-packages/steembase/http_client.py", line 213, in _return
    raise RPCError(error_message)
steembase.exceptions.RPCError: 10 assert_exception: Assert Exception
itr->vote_percent != o.weight: You have already voted in a similar way.

I want you to look into that last line of this error print out really close. You will notice the line itr->vote_percent != o.weight: You have already voted in a similar way.
What this means is that the blockchain throws an error when you try to vote the exact same way twice. Now there are a few ways to prevent this error from being thrown but due to something called out-of-order execution which is very complex (and kind of a big deal in the security realm right now) any safe guards you put up have the potential to through this error even if it was never called in the first place. So to prevent this grief from crashing out program, we have a very eloquent solution. We surround it in a try and catch and usually just throw out the error. Here is what I mean:

from steem import Steem
from steem.post import Post

def loop():
    account = input("Enter Account: ")
    posting_key = input("Enter Key: ")
    s = Steem(keys=posting_key)
    while 1:
        link = input("Enter Link: ")
        link = link.replace(link[0:int(link.find('@'))],'')
        vw = float(input("Enter Voting Weight: "))
        pst = Post(link, s)
        try:
                pst.vote(vw, account)
                print('Voted!')
        except:
                i=5


loop()

So the try and catch (or in python, try and except) tries to run a bit of code but if an exception is thrown it will catch it. Now you can do many things in the exception side of things with the exception, but for simplicity I am just making a variable i and setting it equal to 5. Why? Because I do not care about the exceptions for the time being. Though it may be more correct to do something like this:

try:
        #do something
except Exception,e:
        print("Error: " + str(e))

This will tell you if something is going wrong with your code and what is going on, you can do a lot of things with the exception but I am not going to care too much right now. Once you all have more practice with python and messing around with this bot, maybe you can go and try a bunch of cases to find a bunch of different exceptions and make it do specific things on specific failures.

This Post Is Not Just About Try and Catch (Except)

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