python通过自定义isnumber函数判断字符串是否为数字的方法

''' isnumeric.py
test a numeric string s if it's usable
for int(s) or float(s)
'''
def isnumeric(s):
 '''returns True if string s is numeric'''
 return all(c in "0123456789.+-" for c in s)
# test module ...
if __name__ == '__main__':
 print(isnumeric('123')) # True
 print(isnumeric('-123.45')) # True
 print(isnumeric('+3.14')) # True
 print(isnumeric('$99.95')) # False