l = map(chr, xrange(256)) #将ascii转为字符串
_idmap = str('').join(l)
del l
# Construct a translation string
_idmapL = None #定义一个全局变量
def maketrans(fromstr, tostr):
"""maketrans(frm, to) -> string
Return a translation table (a string of 256 bytes long)
suitable for use in string.translate. The strings frm and to
must be of the same length.
"""
if len(fromstr) != len(tostr):
raise ValueError, "maketrans arguments must have same length"
global _idmapL
if not _idmapL:
_idmapL = list(_idmap) #将ascii 字符串转换为列表
L = _idmapL[:] #列表对象浅拷贝，目的是为了不影响global , or [x for x in _idmapL] or L = list(_idmapL) or L = copy.copy(_idmapL)
fromstr = map(ord, fromstr) #功能与chr相反,即将char转换为对应的数字编码
for i in range(len(fromstr)):
L[fromstr[i]] = tostr[i] #替换
return ''.join(L) #重组
