CLI desktop calculator

def cli():
    print "Welcome to CLI v0.0."
    print "This may be extremely buggy. Enter q to quit."
    stack,functions,prescision=[],{},3
    while True:
        cmd=raw_input('>>')
        if cmd=='':
            pass
        elif cmd.count(':') == 1:
            z=cmd.index(':')
            a,b=cmd[:z],cmd[z+1:]
            m=errorcheck(b,functions)
            if m==1:
                functions[a]=b
        elif cmd[0]=='p':
            if len(cmd[1:])==0:
                print "The prescision is currently set to {0}.".format(prescision)
            elif len(filter(lambda x: not x in ' 0123456789',cmd[1:]))==0:
                prescision=int(cmd[1:])
                print 'The prescision has been set to {0}.'.format(prescision)
            else:
                print 'Invalid requested prescision.'
        elif cmd=='q':
            print "Goodbye!"
            break
        elif cmd=='c':
            v=raw_input('Are you sure you want to clear the stack?\n-->')
            if v in ['y','yes']:
                stack=[]
        else:
            initialstack=stack
            z=run(cmd,stack,prescision,functions)
            if z==0:
                stack=initialstack
            else:
                stack=z
        if len(stack)>5:
            print '...'
            for i in range(5):
                print stack[i+len(stack)-5]
        else:
            for i in stack:
                print i

def run(cmds, stack, prescision, functions):
    l,z=cmds.rsplit(' '),errorcheck(cmds,functions)
    if z==0:
        return 0
    for i in l:
        if stack==0:
            break
        elif i in functions.keys():
            stack = run(functions[i],stack,prescision,functions)
        elif i in '+-*/' or i=='**':
            if len(stack)<2:
                print 'Stack underflow error'
                return 0
            else:
                a=stack.pop()
                b=stack.pop()
                stack.append(round(eval(str(b)+i+str(a)),prescision))
        elif i=='$':
            if len(stack)==0:
                print 'Stack underflow error'
                return 0
            else:
                stack.append(stack[-1])
        elif i=='@':
            if len(stack)<3:
                print 'Stack underflow error'
                return 0
            else:
                z=stack[:-3]
                z.append(stack[-2])
                z.append(stack[-1])
                z.append(stack[-3])
                stack=z
        elif i=='\\':
            if len(stack)<2:
                print 'Stack underflow error'
                return 0
            else:
                a=stack.pop()
                b=stack.pop()
                stack.append(a)
                stack.append(b)
        elif i=='%':
            if len(stack)==0:
                print 'Stack underflow error'
                return 0
            else:
                stack.pop()
        elif len(filter(lambda x: not x in '.0123456789',i))==0:
            stack.append(round(float(i),prescision))
    return stack

def errorcheck(cmds, functions):
    l=cmds.rsplit(' ')
    for i in l:
        if i.count('.')>1:
            print 'Invalid decimal placing.'
            return 0
        if not i in '\\$%@+-*/' and i!='**' and not i in functions.keys():
            if len(filter(lambda x: not x in '.0123456789',i))!=0:
                print "Undefined command {0}".format(i)
                return 0
    return 1