下面的代码内容是关于python检查字符串是否是正确的ISBN的代码，希望能对各朋友也有帮助。

def isISBN(isbn):  
    """Checks if the passed string is a valid ISBN number."""  
    if len(isbn) != 10 or not isbn[:9].isdigit():  
        return False  
    if not (isbn[9].isdigit() or isbn[9].lower() == "x"):  
        return False  
  
  
    checksum = (11 - tot % 11) % 11  
    if isbn[9] == 'X' or isbn[9] == 'x':  
        return checksum == 10  
    else:  
        return checksum == int(isbn[9])  
  
ok = """031234161X 0525949488 076360013X 0671027360 0803612079 
        0307263118 0684856093 0767916565 0071392319 1400032806 0765305240"""  
for code in ok.split():  
    assert isISBN(code)  
  
bad = """0312341613 052594948X 0763600138 0671027364 080361207X 0307263110 
         0684856092 0767916567 0071392318 1400032801 0765305241 031234161 
         076530Y241 068485609Y"""  
for code in bad.split():  
    assert not isISBN(code)  
  
print "Tests of isISBN()passed."