新手求助，这个程序是从书上看到的，运行不出来。

这个程序是自动产生规定行*列的随机数，但是我的不知道为什么都运行不出来？
import random
def get_int(msg,minimum,default):
    while True:
        try:
            line=input(msg)
            if not line and default is not None:
                return default
            i=int(line)
            if i<minimum:
                print("must be >=",minimum)
            else:
                return i
        except ValueError as err:
            print(err)
rows=get_int("rows:",1,None)
columns=get_int("columns:",1,None)
minimum=get_int("minimum(or Enter for 0):",-1000000,0)
default=1000
if default<minimum:
    default=2*minimum
maximum=get_int("maximum(or Enter for"+str(default)+"):",minimum,default)
row=0
while row<rows:
    line=""
    column=0
    while column<columns:
        i=random.randint(minimum,maximum)
        s=str(i)
        while len(s)<10:
            s=""+s
        line+=s
        column+=1
    print(line)
    row+=1