Can only concatenate str not nonetype to str ошибка

Судя по тексту ошибки, в одном из row[i] — находится None.

Воспроизведение ошибки:

In [48]: "string" + None
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-48-69dded62479b> in <module>
----> 1 "string" + None

TypeError: can only concatenate str (not "NoneType") to str

Для того, чтобы вычитать результат запроса ("SELECT ..."), выполненного при помощи cursor.execute(SQL), надо воспользоваться методом cursor.fetchone() или cursor.fetchall():

cursor.execute(query)
for row in cursor.fetchall():
    # ...

или воспользоваться однострочником:

for row in cursor.execute(query).fetchall():
    # ...

UPD: внимательнее присмотрелся к вашему запросу — если я правильно понял и ваша цель — получить единственную строку (TOP 1), то можно обойтись без цикла:

qry = '''SELECT TOP 1
           className, eqpName, partName, nodeName, core, opisanie, serviceName, FIO
         FROM smsTelegram
         ORDER BY problemID DESC'''  

text = None
row = cursor.execute(qry).fetchone()
if row:
    text = '<b>Класс проблемы: </b>{}'
            'n<b>Оборудование: </b>{}'
            'n<b>Часть оборудования: </b>{}'
            'n<b>Узел: </b>{}'
            'n<b>Суть: </b>{}'
            'n<b>Детали: </b>{}'
            'n<b>Служба: </b>{}'
            'n<b>Специалист: </b>{}'
    text = text.format(*row).replace("<br>", " ")

Это значит, что вы пытаетесь сложить строки с числами

Программист освоил JavaScript и начал изучать Python. Чтобы освоиться в языке, он переносит проекты с одного языка на другой — убирает точки с запятой, добавляет отступы и меняет команды одного языка на такие же команды из другого языка.

Один из фрагментов его кода после перевода в Python выглядит так:

# зарплата в месяц
month = 14200
# плата за ЖКХ
regular_cost = 5800

# функция, которая считает и возвращает долю ЖКХ в бюджете
def calculate(budget,base):
    message = 'На коммунальные платежи уходит ' + base + 'р. - это ' + base/budget*100 + ' процентов от ежемесячного бюджета'
    return message
    
# отправляем в функцию переменные и выводим результат на экран
print(calculate(month,regular_cost))

Но после запуска программист получает ошибку:

❌ TypeError: can only concatenate str (not «int») to str

Странно, но в JavaScript всё работало, почему же здесь код сломался?

Что это значит: компилятор не смог соединить строки и числа, поэтому выдал ошибку.

Когда встречается: в языках со строгой типизацией, например в Python, когда у всех переменных в выражении должен быть один и тот же тип данных. А вот в JavaScript, который изучал программист до этого, типизация нестрогая, и компилятор сам мог привести все части выражения к одному типу.

Что делать с ошибкой TypeError: can only concatenate str (not «int») to str

Раз это проблема строгой типизации, то для исправления этой ошибки нужно просто привести все части к одному типу. 

В нашем случае мы хотим получить на выходе строку, поэтому все слагаемые должны быть строкового типа. Но base и base/budget*100 — это числа, поэтому просто так их сложить со строками не получится. Чтобы выйти из ситуации, явно преобразуем их в строки командой str():

message = 'На коммунальные платежи уходит ' + str(base) + 'р. - это ' + str(base/budget*100) + ' процентов от ежемесячного бюджета'

Команда str() делает так, что всё внутри неё приводится к строке и она отдаёт дальше строку. В итоге операция склейки строк проходит как ожидаемо: строка к строке даёт строку. Нет повода для беспокойства. 

If you are getting trouble with the error “TypeError: can only concatenate str (not “NoneType”) to str” in Python, do not worry. Today, our article will give some solutions and detailed explanations to handle the problem. Keep on reading to get your answer.

Why does the error “TypeError: can only concatenate str (not “NoneType”) to str” in Python occur?

TypeError is an exception when you apply a function or operation to objects of the wrong type. “TypeError: can only concatenate str (not “NoneType”) to str” in Python occurs when you try to concatenate a variable that has the type None and a variable that belongs to the string type. Look at the simple example below that causes the error.

Code:

myStr = "string"
myNone = None

print(myStr + myNone)

Result:

TypeError Traceback (most recent call last)
 in <module>
----> 4 print(myStr + myNone)
TypeError: can only concatenate str (not "NoneType") to str

This is a very simple example to show you the error. We all know that we can not apply operators to different variables in the Python programming language. In this situation, we can join a string type and a None Type. 

Now you are clear about the root of the problem. We will look at another example causing the error people often get when working with Object Oriented Programming.

Code:

# Create Class student to store name and age
class Student:
  def __init__(self, name, age):
    self.__name = name
    self.__age = age
 
  def showName(self):
    print(self.__name)
 
  def showAge(self):
    print(self.__age)
  
student1 = Student("Helen Kang", 15)
print("My name is" + student1.showName())

Result:

Helen Kang
Traceback (most recent call last):
  line 14, in <module>
    print("My name is" + student1.showName())
TypeError: can only concatenate str (not "NoneType") to str

Let’s move on. We will discover solutions to this problem.

Solutions to the problem

Add a new function

As you can see, the method in the example is a non-return function because they return nothing but print the string. When called, the method returns nothing, and its result belongs to the class NoneType. Let’s check the type of the function showName().

Code:

print(type(student1.showName()))

Result:

<class 'NoneType'>

We need to create a new method that returns the name to fix the error. This method will be valid to be called in the print function. 

Code:

# Create Class student to store name and age
class Student:
  def __init__(self, name, age):
    self.__name = name
    self.__age = age
 
  def showName(self):
    print(self.__name)
 
  def showAge(self):
    print(self.__age)
  
  def getName(self):
    return self.__name
  
student1 = Student("Helen Kang", 15)
print("My name is " + student1.getName())

Result:

My name is Helen Kang

You can also use the comma or format string to get the same result:

print("My name is", student1.getName())

print(f"My name is {student1.getName()}")

Call the function without the print function

Because the function is to print the name, you do not need to call it in the print function. We will only print the introduction string and call the function to print the name alone. To not print the new line, use syntax end = ‘ ‘.

Code:

# Create Class student to store name and age
class Student:
  def __init__(self, name, age):
    self.__name = name
    self.__age = age
 
  def showName(self):
    print(self.__name)
 
  def showAge(self):
    print(self.__age)
    
student1 = Student("Helen Kang", 15) 
print("My name is", end = ' ')
student1.showName()

Result:

My name is Helen Kang

Summary

Our article has explained the error “TypeError: can only concatenate str (not “NoneType”) to str” in Python and showed you the root of the problem. Understanding each function’s returned type is necessary to avoid errors.

Maybe you are interested:

• How To Resolve TypeError: ‘in ‘ Requires String As Left Operand, Not Int In Python
• How To Resolve TypeError: Object Of Type Float32 Is Not JSON Serializable In Python
• How To Resolve TypeError: ‘numpy.float64’ Object Is Not Iterable In Python

In this article, we will discuss what the typeerror: can only concatenate str not nonetype to str error message means and why it occurs.

We will also provide some solutions to troubleshoot and fix this error in your Python code.

Why does the TypeError: can only concatenate str (not “NoneType”) to str occurs?

The TypeError: can only concatenate str (not “NoneType”) to str occurs because you’re trying to concatenate a string with a None value or a variable that has no value assigned to it.

In addition, this error occur if you are trying to concatenate a None value with a string which is the Python cannot determine the data type of the None value, leading to a TypeError.

Here is an example on how the error occur:

name = None
greeting = "Hello " + name
print(greeting)

This example program will creates a variable name and assigns it the value None.

Then, it creates a variable greeting and concatenates the string “Hello” with the value of the name variable using the “+“ operator.

Since name has a value of None, the concatenation will result in an error due to the inability to concatenate a string with a None value.

Finally, the print() function is called to print the value of the greeting variable, which will fail due to the error.

So, Python cannot determine the data type of the name variable and throws the error message:

Traceback (most recent call last):
File “C:UsersDellPycharmProjectspythonProjectmain.py”, line 2, in
greeting = “Hello ” + name
TypeError: can only concatenate str (not “NoneType”) to str

How to solve this error can only concatenate str not nonetype to str?

Now that you understand the error why it is occur, then let’s take a look at some solutions on how to solve it.

Solution 1: Avoid Concatenating a None Value with a String

The first solution to solve this error is that you will need to check first the value of your variable using an if statement to avoid concatenating a None with a string.

If the variable is not None, then it will concatenate the variable to a string as follows:

name = "Juan Delacruz"

if name is not None:
    print("The value of name is " + name)
else:
    print("The value of name is None")

This example code, will checks if the variable name has a value assigned to it.

If name is not None, it will print a message that includes the value of name concatenated with the string “The value of name is “.

If name has no value (i.e., it is None), it will print a message that says “The value of name is None“.

In this case, name has the value “John”, so the message “The value of name is John” will be printed to the console.

The value of name is Juan Delacruz

Solution 2: Using a Default Value for the Variable

For the second solution to solve this error is to use a default value for the variable if the value is none.

For example:

age = None

if age is None:
    age = 25

print("The value of age is " + str(age))

This example code will sets the variable “age” to None, then checks if it is None.

Then, if it is None, it will sets the value of “age” to 25.

Finally, it will prints the value of “age” as a string.

In this case, the output will be:

The value of age is 25

Through adding a default value to change None, you will assure that the TypeError: can only concatenate str (not “NoneType”) to str will be avoided.

In Python, None is a special value that represents the absence of a value. It is often used to indicate that a variable or argument has not been assigned a value or that a function does not return anything.

Note: In order to prevent a TypeError, it is important to understand when Python produces a None value and then handle it appropriately within your code.

Solution 3: Convert None value to a string

Another way to solve the TypeError: can only concatenate str (not “NoneType”) to str error message is to convert the None value to a string before concatenating it with the string.

For example, let’s say you have the following code:

name = None
greeting = "Hello " + str(name)
print(greeting)

In this example code, we are converting the None value to a string using the str() function before concatenating it with the string.

This way, we are assuring that the None value is converted to a string before concatenating, and the TypeError will be prevented.

Solution 4: Use f-strings or string formatting

Another way to concatenate strings in Python without encountering the error can only concatenate str (not “NoneType”) to str error message is to use f-strings or string formatting.

For example:

name = None
greeting = f"Hello {name}"

In this example code, we are using f-strings to concatenate the string and the variable.

F-strings are a new and more convenient way to format strings in Python 3.6 and later versions.

They allow us to embed expressions inside string literals, using {} characters.

Alternatively, we can also use string formatting to concatenate strings and variables.

For example:

name = None
greeting = "Hello {}".format(name)

In this code, we are using string formatting to concatenate the string and the variable.

String formatting allows you to embed variables and expressions inside string literals, using {} characters and the format() method.

Common cause of None value if you run a Python program are:

• Assigning None to a variable directly
• Call a function that returns null
• Call a function that returns only under a sure condition

If you are calling a function which have no return statement, the function will return a None value automatically.

For example:

def greet():
    pass


result = greet()
print(result)

If a function doesn’t have a return statement explicitly defined, the function will return the value None.

Also, we can use conditional return statement to get a None.

For example:

def welcome(name):
    
    if name:
       
        return f"Hello {name}!"
result1 = welcome("")
print(result1)

result2 = welcome("Nathan")
print("n" in result2)

• def welcome(name):
  • Declare a function that greets the given name.
• if name:
  • Check if the name is not empty
• return f”Hello {name}!”:
  • If the name is not empty, return a greeting message.
• result1 = welcome(“”):
  • Call the welcome function with an empty string as the argument.
• print(result1):
  • The output of the function will be None, since the input name is empty.
• result2 = welcome(“Nathan”)
  • Call the welcome function with a non-empty string as the argument.
• print(“n” in result2)
  • Check if the character ‘n’ is present in the output string.

Additional Resources

Here are some additional resources that can help you learn more about the error message and other common Python errors:

• Typeerror: can only concatenate str not bytes to str [FIXED]
• Typeerror can’t concat str to bytes
• Typeerror: expected string or bytes-like object [SOLVED]

Conclusion

In this article, we have explained what the typeerror can only concatenate str not nonetype to str error message means and why it occurs.

We have also provided some solutions to troubleshoot and solve this error in your Python code.

FAQs