Str error python

So you have encountered the exception, i.e., TypeError: ‘str’ object is not callable. In the following article, we will discuss type errors, how they occur and how to resolve them.

What is a TypeError?

The TypeError occurs when you try to operate on a value that does not support that operation. The most common reason for an error in a Python program is when a certain statement is not in accordance with the prescribed usage. The Python interpreter immediately raises a type error when it encounters an error, usually along with an explanation. For instance:

val1 = 100
val2 = "random text"

print(val1/val2)

When you try to divide an integer value with a string, it results in a type error.

Like any TypeError, the ‘str’ object is not callable occurs when we try to perform an operation not supported by that datatype. In our case, here it’s the ‘string’ datatype. Let’s see some examples of where it can occur and how we can resolve them.

Example 1:

str = "This is text number 1"
string2 = "This is text number 2"

print(str(str) + string2)

In the code above, we have deliberately defined the first variable name with a reserved keyword called str. Moreover, the second variable, string2, follows Python’s naming conventions. In the print statement, we use the str method on the str variable, this confuses the Python’s interpreter, and it raises a type error, as shown in the image below.

Example 2:

string1 = "This is text number 1"
string2 = "This is text number 2"

print("%s %s" (string1,string2))

Contrary to example 1, where we had defined a variable with the str reserved keyword, which raised an error. In the example 2 code, we are using the ‘ % ‘ operator to perform string formatting. However, there is a minor issue in the syntax. We have omitted the % before the tuple. Missing this symbol can raise a similar error.

How to resolve this error?

The solution to example 1:

In Python, the str() function converts values into a string. It takes an object as an argument and converts it into a string. The str is a pre-defined function and also a reserved keyword. Therefore, it can’t be used as a variable name as per Python’s naming conventions.

To resolve the error, use another variable name.

string1 = "This is text number 1"
string2 = "This is text number 2"

print(str(string1) + string2)

The solution to example 2:

In example 2, we tried to use string formatting to display string1 and string2 together. However, not using the % operator before the tuples of values TypeError: ‘str’ object is not a callable error that gets thrown. To resolve it, use the % operator in its proper place.

string1 = "This is text number 1"
string2 = "This is text number 2"

print("%s %s" %(string1,string2))

TypeError: ‘str’ object is not callable Selenium

This error is likely due to accidentally invoking a function() which is actually a property. Please check your code for this.

TypeError ‘str’ object is not callable BeautifulSoup/Django/Collab

Irrespective of the library used, this error can creep in if you have used some reserved keyword as a variable or redefined some property or a function of the library. Please check your code for such things.

TypeError ‘str’ object is not callable matplotlib

Somewhere in the code, you might have used plt.xlabel = “Some Label”. This will change the import of matplotlib.pyplot. Try to close the Notebook and restart your Kernel. After the restart, rerun your code, and everything should be fine.

FAQs

Conclusion

In this article, we discussed where the ‘str’ object is not callable error can occur and how we can resolve it. This is an easy error to fix. We must ensure we don’t use the reserved keywords for naming variables. In addition, we also have to avoid redefining default methods.

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Strings are immutable objects, which means you cannot change them once created. If you try to change a string in place using the indexing operator [], you will raise the TypeError: ‘str’ object does not support item assignment.

To solve this error, you can use += to add characters to a string.

a += b is the same as a = a + b

Generally, you should check if there are any string methods that can create a modified copy of the string for your needs.

This tutorial will go through how to solve this error and solve it with the help of code examples.

Python TypeError: ‘str’ object does not support item assignment

Let’s break up the error message to understand what the error means. TypeError occurs whenever you attempt to use an illegal operation for a specific data type.

The part 'str' object tells us that the error concerns an illegal operation for strings.

The part does not support item assignment tells us that item assignment is the illegal operation we are attempting.

Strings are immutable objects which means we cannot change them once created. We have to create a new string object and add the elements we want to that new object. Item assignment changes an object in place, which is only suitable for mutable objects like lists. Item assignment is suitable for lists because they are mutable.

Let’s look at an example of assigning items to a list. We will iterate over a list and check if each item is even. If the number is even, we will assign the square of that number in place at that index position.

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

for n in range(len(numbers)):
    if numbers[n] % 2 == 0:
        numbers[n] = numbers[n] ** 2
print(numbers)

Let’s run the code to see the result:

[1, 4, 3, 16, 5, 36, 7, 64, 9, 100]

We can successfully do item assignment on a list.

Let’s see what happens when we try to change a string using item assignment:

string = "Research"
string[-1] = "H"
print(string)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-3-e8e5f13bba7f> in <module>
      1 string = "Research"
----> 2 string[-1] = "H"
      3 print(string)

TypeError: 'str' object does not support item assignment

We cannot change the character at position -1 (last character) because strings are immutable. We need to create a modified copy of a string, for example using replace():

string = "Research"
new_string = string.replace("h", "H")
print(new_string)

In the above code, we create a copy of the string using = and call the replace function to replace the lower case h with an upper case H.

ResearcH

Let’s look at another example.

Example

In this example, we will write a program that takes a string input from the user, checks if there are vowels in the string, and removes them if present. First, let’s define the vowel remover function.

def vowel_remover(string):

    vowels = ["a", "e", "i" , "o", "u"] 

    for ch in range(len(string)):

        if string[ch] in vowels:

            string[ch] = ""

    return string

We check if each character in a provided string is a member of the vowels list in the above code. If the character is a vowel, we attempt to replace that character with an empty string. Next, we will use the input() method to get the input string from the user.

string = input("Enter a string: ")

Altogether, the program looks like this:

def vowel_remover(string):

    vowels = ["a", "e", "i", "o", "u"] 

    for ch in range(len(string)):

        if string[ch] in vowels:

            string[ch] = ""

    return string

string = input("Enter a string: ")

new_string = vowel_remover(string)

print(f'String with all vowels removed: {new_string}')

Let’s run the code to see the result:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-6-7bd0a563e08b> in <module>
      8 string = input("Enter a string: ")
      9 
---> 10 new_string = vowel_remover(string)
     11 
     12 print(f'String with all vowels removed: {new_string}')

<ipython-input-6-7bd0a563e08b> in vowel_remover(string)
      3     for ch in range(len(string)):
      4         if string[ch] in vowels:
----> 5             string[ch] = ""
      6     return string
      7 

TypeError: 'str' object does not support item assignment

The error occurs because of the line: string[ch] = "". We cannot change a string in place because strings are immutable.

Solution #1: Create New String Using += Operator

We can solve this error by creating a modified copy of the string using the += operator. We have to change the logic of our if statement to the condition not in vowels. Let’s look at the revised code:

def vowel_remover(string):

    new_string = ""

    vowels = ["a", "e", "i", "o", "u"] 

    for ch in range(len(string)):

        if string[ch] not in vowels:

            new_string += string[ch]

    return new_string

string = input("Enter a string: ")

new_string = vowel_remover(string)

print(f'String with all vowels removed: {new_string}')

Note that in the vowel_remover function, we define a separate variable called new_string, which is initially empty. If the for loop finds a character that is not a vowel, we add that character to the end of the new_string string using +=. We check if the character is not a vowel with the if statement: if string[ch] not in vowels.

Let’s run the code to see the result:

Enter a string: research
String with all vowels removed: rsrch

We successfully removed all vowels from the string.

Solution #2: Create New String Using str.join() and list comprehension

We can solve this error by creating a modified copy of the string using list comprehension. List comprehension provides a shorter syntax for creating a new list based on the values of an existing list.

Let’s look at the revised code:

def vowel_remover(string):

    vowels = ["a", "e", "i", "o", "u"] 

    result = ''.join([string[i] for i in range(len(string)) if string[i] not in vowels])

    return result

string = input("Enter a string: ")

new_string = vowel_remover(string)

print(f'String with all vowels removed: {new_string}')

In the above code, the list comprehension creates a new list of characters from the string if the characters are not in the list of vowels. We then use the join() method to convert the list to a string. Let’s run the code to get the result:

Enter a string: research
String with all vowels removed: rsrch

We successfully removed all vowels from the input string.

Summary

Congratulations on reading to the end of this tutorial. The TypeError: ‘str’ object does not support item assignment occurs when you try to change a string in-place using the indexing operator []. You cannot modify a string once you create it. To solve this error, you need to create a new string based on the contents of the existing string. The common ways to change a string are:

• List comprehension
• The String replace() method
• += Operator

For further reading on TypeErrors, go to the articles:

• How to Solve Python TypeError: object of type ‘NoneType’ has no len()
• How to Solve Python TypeError: ‘>’ not supported between instances of ‘str’ and ‘int’
• How to Solve Python TypeError: ‘tuple’ object does not support item assignment
• How to Solve Python TypeError: ‘set’ object does not support item assignment

To learn more about Python for data science and machine learning, go to the online courses page on Python for the most comprehensive courses available.

Have fun and happy researching!

Представим такое: студент только что окончил школу, где изучал Паскаль. В универе на лабораторной по Python ему дали такое задание: заменить в строке все точки на восклицательные знаки.

Студент помнит, что можно обращаться к отдельным элементам строки, поэтому сразу пишет очевидный цикл:

# исходная строка, где нужно заменить точки
s = 'Привет. Это журнал «Код».'
# делаем цикл, который переберёт все порядковые номера символов в строке
for i in range(len(s)):
    # если текущий символ — точка
    if s[i] == '.':
        # то меняем её на восклицательный знак    
        s[i] = '!'

Но после запуска компьютер выдаёт ошибку:

❌  TypeError: ‘str’ object does not support item assignment

Казалось бы, почему? Есть строка, можно обратиться к отдельным символам, цикл в порядке — что не так-то?

Что это значит: интерпретатор сообщает нам, что не может поменять символ в строке один на другой.

Когда встречается: когда в Python мы пытаемся напрямую заменить символ в строке, как это делали в Паскале или некоторых других языках, которые это умеют. В Python строки хоть и состоят из символов, которые можно прочитать по отдельности, но управлять этими символами он не даёт. 

Что делать с ошибкой TypeError: ‘str’ object does not support item assignment

Решение простое: нужно не работать с символами в строке напрямую, а собирать новую строку из исходной. А всё потому, что Python разрешает прибавлять символы к строке, считая их маленькими строками. Этим и нужно воспользоваться:

# исходная строка, где нужно заменить точки
s = 'Привет. Это журнал «Код».'
# строка с результатом
r = ''
# делаем цикл, который переберёт все порядковые номера символов в исходной строке
for i in range(len(s)):
    # если текущий символ — точка
    if s[i] == '.':
        # то в новой строке ставим на её место восклицательный знак    
        r = r + '!'
    else:
        # иначе просто переносим символ из старой строки в новую
        r = r + s[i]
# выводим результат
print(r)

Но проще всего, конечно, использовать встроенную функцию replace():

# исходная строка, где нужно заменить точки
s = 'Привет. Это журнал «Код».'
# встроенной функцией меняем точки на восклицательные знаки
s = s.replace('.','!')
# выводим результат
print(s)