英文:
In python, why a variable which is assigned an integer value in a function but outside for loop ,return type as string
问题
以下是代码，我想返回字典中值的最大长度。
def longest_value(d={}):
max_len = 0
for k, v in d.items():
if len(v) > max_len:
max_len = len(v)
return max_len
if __name__ == '__main__':
fruits = {'fruit': 'apple', 'color': 'orange'}
print(longest_value(fruits))
当运行此代码时，抛出的错误是：Type Error。但是，如果我检查 max_len 的类型，它返回字符串，即使我将其分配为全局变量仍然会抛出相同的错误。如果我在 for 循环内部分配变量，它可以工作，但我想知道为什么在第一种情况下不起作用，需要遵循哪些规则。
尽管这个问题可能相当简单，但在发帖之前我已经努力搜索答案，但没有成功。所以感谢任何关于这个问题的帮助。谢谢。
英文:
Here is the code, where I want to return the value in the dictionary with maximum length.
The code goes as follows:
def longest_value(d={}):
max_len = 0
for k,v in d.items():
if len(v) > max_len:
max_len = v
return max_len
if __name__ == '__main__':
fruits = {'fruit': 'apple', 'color': 'orange'}
print(longest_value(fruits))
When I run this code, the error thrown is:
however, if I check the type for max_len it returns string, even if I assign it as global still it throws the same error.
If I assign the variable inside the for loop it works, but I want to know why it is not working in the first case, what are the rules which needs to be followed here.
Though this question could be pretty lame, but I tried hard before posting, to search for an answer online, but I dint succeed. So appreciate any help on this.
Thanks
答案1
得分: 3
第一次迭代会得到例如：
k, v = 'fruit', 'apple'
然后你设置 max_len = 'apple'。在下一次迭代中，你会得到
k, v = 'color', 'orange'
然后你会问 len('orange') > 'apple'。左边是一个整数，右边是一个字符串。
如果你在循环内部设置 max_len = 0，你每次都会重置计数器（len(v) > 0），所以函数总是返回最后一个项目。
英文:
The first iteration gives you e.g.
k, v = 'fruit', 'apple'
and you set max_len = 'apple'. In the next iteration, you get
k, v = 'color', 'orange'
and you ask if len('orange') > 'apple'. The left side is an integer, the right one is a string.
If you set max_len = 0 inside the loop, you reset the counter each time (len(v) > 0), so the function always returns the last item.
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