python中如何将数字转字符串

'%f' % 1234.567890   输出：'1234.567890'

'%.2f' % 1234.567890  输出：'1234.57'

str(5)

>>> '10'+str(4)

'104'

>>> str='hello'

>>> '10'+str(4)

Traceback (most recent call last):

 File "<pyshell#25>", line 1, in <module>

  '10'+str(4)

TypeError: 'str' object is not callable

>>>