The following Python script works well with Python 2.3 and Python 2.4 (which don't have a built-in definition of all():

#! /usr/bin/env python
# vim: set fileencoding=utf-8
# (c) Uwe Kleine-König
# GPLv2

import locale
import sys

f = file(sys.argv[1])
data = f.read()

def len_utf8_char(data):
    if not 'all' in dir(__builtins__):
        def all(seq):
            for i in seq:
                if not i:
                    return False
            return True

    def check_cont(num):
        if all(map(lambda c: ord(c) >= 0x80 and ord(c) <= 0xbf, data[1:num])):
            return num
        else:
            return -1

    if ord(data[0]) < 128:
        # ASCII char
        return 1
    elif ord(data[0]) & 0xe0 == 0xc0:
        return check_cont(2)
    elif ord(data[0]) & 0xf0 == 0xe0:
        return check_cont(3)
    elif ord(data[0]) & 0xf8 == 0xf0:
        return check_cont(4)
    elif ord(data[0]) & 0xfc == 0xf8:
        return check_cont(5)
    elif ord(data[0]) & 0xfe == 0xfc:
        return check_cont(6)

i = 0
maxl = 0
while i < len(data):
    l = len_utf8_char(data[i:])
    if l < 0:
        prefenc = locale.getpreferredencoding()
        if prefenc not in ('UTF-8', 'ANSI_X3.4-1968'):
            print prefenc
        else:
            print 'ISO-8859-1'
        sys.exit(0)

    if maxl < l:
        maxl = l
    i += l

if maxl > 1:
    print 'UTF-8'
else:
    print 'ANSI_X3.4-1968'

Now with Python 2.5 and later this fails as follows:
$ python2.5 guess-charmap guess-charmap
Traceback (most recent call last):
  File "guess-charmap", line 43, in <module>
    l = len_utf8_char(data[i:])
  File "guess-charmap", line 30, in len_utf8_char
    return check_cont(2)
  File "guess-charmap", line 21, in check_cont
    if all(map(lambda c: ord(c) >= 0x80 and ord(c) <= 0xbf, data[1:num])):
NameError: free variable 'all' referenced before assignment in enclosing scope

删除all的兼容性定义修复了Python 2.5+的问题。
我想知道,在这种情况下,Python为什么不选择内置的all()。?

最佳答案

当Python解析函数体时,它会查找赋值中使用的变量名。除非使用global变量声明,否则所有这些变量都假定为局部变量。
def all为变量名all赋值。尽管赋值在if-block中,但在所有情况下,all都被视为局部变量(无论if-block是否稍后执行)。
如果不执行if块,all将成为未绑定的局部变量,从而引发NameError。
If you move the if not 'all' ... block outside the def len_utf8_char, then
你会避免这个问题的。

关于python - Python比内置函数更喜欢未分配的局部函数,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/6617354/

10-12 12:40
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