在Python中赋值之前引用的局部变量

Question

Truel=""
count = 0
finle_touch=False #true after it find the first 3 upperletter

# check if there is 1 lower letter after three upper letter
def one_lower(i):
    count=0
    if i == i.lower:
        finle_touch=True
        Truel=i

# check for 3 upper letter
def three_upper(s):
    for i in s:
        if count == 3:
            if finle_touch==True:
                break
            else:
                one_lower(i)
        elif i == i.upper:
            count +=1
            print(count) #for debug
        else:
            count ==0
            finle_touch=False

stuff="dsfsfFSfsssfSFSFFSsfssSSsSSSS......."
three_upper(stuff)
print(Truel)

所以我在'stuff'上有很多字符串,我喜欢找到1个用大写字母表示的小写字母.

但当我运行此代码时,我得到:

Traceback (most recent call last):
  File "C:\Python33\mypy\code.py", line 1294, in <module>
    three_upper(stuff)
  File "C:\Python33\mypy\code.py", line 1280, in three_upper
    if count == 3:
UnboundLocalError: local variable 'count' referenced before assignment

我不明白为什么.提前致谢

Answer 1

由于这行,count +=1python认为这count是一个局部变量,并且在您使用时不会搜索全局范围if count == 3:.这就是你得到那个错误的原因.

使用global语句来处理:

def three_upper(s): #check for 3 upper letter
    global count
    for i in s:

来自docs:

函数中的所有变量赋值都将值存储在本地符号表中; 而变量引用首先在本地符号表中查找,然后在全局符号表中查找,然后在内置名称表中查找.因此,全局变量不能直接在函数内赋值(除非在全局语句中命名),尽管可以引用它们.