'str'对象没有属性'len' [英] 'str' object has no attribute 'len'

问题描述

通过检查前三个字母/数字并确保它们相同之前，我已经有了一种可以正常工作的方法

Ive got a method that use to work by checking the first three letters/numbers and making sure they are the same before it continues like so

def combineProcess(request):
    carID1 = request.POST['carID1']
    carID2 = request.POST['carID2']
    for x in range (0,3):
        a += carID1.length(x)
        b += carID2.length(x)
    if a.equals(b):
        //do something

在使用之前，现在它停止了，并且出现了这个错误.

before it use to work now it stopped and i get this error.

Exception Type: UnboundLocalError
Exception Value:    

local variable 'a' referenced before assignment

几周前我从未使用过它，但是并没有改变任何东西，所以我将a和b设置为全局.

which i never use to get a few weeks ago didnt change anything so i made a and b global.

def combineProcess(request):
    carID1 = request.POST['carID1']
    carID2 = request.POST['carID2']
    global a,b
    for x in range (0,3):
        a += carID1.length(x)
        b += carID2.length(x)
    if a.equals(b):
        //do something

现在我收到此错误.

Exception Type: NameError
Exception Value:    

name 'a' is not defined

然后我删除了全局行，并把它放在了

Then i removed the global line and just put this

a = "P"

并出现以下错误

str object has no attribute length() or len()

现在让我感到困惑的是，这段代码如何停止工作，为什么不能识别字符串对象具有len()方法.主要是我迷失了我的代码从工作到两周不工作的过程.

which now has me puzzled how has this code stop working and why cant it recognize that a string object has a len() method. mainly I am lost how my code went from working to not working over a two weeks off.

推荐答案

Python字符串len()方法

Python String len() Method

语法

以下是len()方法的语法-

Following is the syntax for len() method −

len( str )

示例

str = "this is string example....wow!!!";
print("Length of the string: ", len(str))

当我们运行上面的程序时，它会产生以下结果-

When we run above program, it produces following result −

Length of the string:  32

参考: Python字符串len()方法

UnboundLocalError:分配前引用了本地变量'a'

UnboundLocalError: local variable 'a' referenced before assignment

说明

这是因为，即使存在a和b，您也正在函数combineProcess()中使用名称为a和b的赋值语句.自然地，这会在函数范围内创建一个名为a和b的变量.

This is because, even though a and b exists, you're also using an assignment statement on the name a and b inside of the function combineProcess(). Naturally, this creates a variable inside the function's scope called a and b.

Python解释器会在模块加载时看到此情况，并决定在本地范围内不应使用a和b的全局范围，这会导致在尝试引用变量之前出现问题本地分配.

The Python interpreter sees this at module load time and decides that the global scope's of a and b should not be used inside the local scope, which leads to a problem when you try to reference the variable before it is locally assigned.

示例

Var1 = 1
Var2 = 0
def function():
    if Var2 == 0 and Var1 > 0:
        print("Result One")
    Var1 =- 1

function()

如果运行此程序，则会出现以下错误.

If you run this program, it gives the following error.

UnboundLocalError: local variable 'Var1' referenced before assignment

由于修改了Var1的值，因此将在函数范围内创建一个名为Var1的变量.结果由于条件检查，在Var1 =- 1语句之前，报告了Var1 > 0错误.

Since, the value of Var1 is modified, this creates a variable inside the function's scope called Var1. As a result error is reported because of the condition check, Var1 > 0 before the Var1 =- 1 statement.

但是，如果我们按如下所示修改代码.

But if we modify the code as follows.

Var1 = 1
Var2 = 0
def function():
    global Var1
    if Var2 == 0 and Var1 > 0:
        print("Result One")
    Var1 =- 1

function()

然后正常工作.

请注意，如果我们将语句Var1 =- 1移到if条件检查之前，那么即使您不使用global Var1语句，它也不会报告任何错误.因此，以下代码可以正常工作.

Note that, if we move the statement Var1 =- 1 before the if condition check, then it will not report any error even if you don't use global Var1 statement. So, the following code works fine.

Var1 = 1
Var2 = 0
def function():
    Var1 =- 1
    if Var2 == 0 and Var1 > 0:
        print("Result One")

function()

参考:请参见 answer .

NameError:名称'a'未定义

NameError: name 'a' is not defined

说明

您可能会收到此错误，因为在Python中，您无法使用equals()方法比较两个字符串.没有这样的方法.

Probably you are getting this error because in Python, you cannot compare two strings using equals() method. There is no such method exists.

示例:比较两个字符串

您可以使用> , < , <= , <= , == , !=比较两个字符串. Python按字典顺序比较字符串，即使用字符的ASCII值.例如，要比较两个字符串是否相等，可以执行以下操作.

You can use > , < , <= , <= , == , != to compare two strings. Python compares string lexicographically i.e using ASCII value of the characters. For example, to compare two strings for equality, you can do as follows.

if string1 == string2:
    // do something

这篇关于'str'对象没有属性'len'的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！