BF shorthand to long

# python 3.4.3
# convert BF shorthand code to standard BF code
# this program can process 1+ or 2>>, but bf_l2s.py will not generate that shorthand

prevch=""
nextch=""
counter=1
error_count=0
command_set="<>+-[].,"
num=""

file = open(input(("bf file: "), 'r')

print()

while True:
    nextch=file.read(1)

    if(not nextch):
        file.close()
        break

    if(nextch.isnumeric()):
        num = num + nextch
    elif(nextch not in command_set):
        error_count += 1
    elif(num == ""):
        print(nextch,end="")
    else:
        print(nextch * int(num), end="")
        num=""
print()
print()

"""
Sample input BF code, Hello World implementations in the Esoteric Programming Language Wiki

++++++++++[>+++++++>++++++++++>+++>+<
<<<-]>++.>+.+++++++..+++.>++.<<++++++
+++++++++.>.+++.------.--------.>+.>.


bf_l2s.py returns:

10+[>7+>10+>3+>+4<-]>++.>+.7+..3+.>++.<<15+.>.3+.6-.8-.>+.>.

111 Commands

bf_s2l.py returns the original program (without formatting), and it runs too!
"""