Ошибка valueerror could not convert string to float

In Python, we can only convert specific string values to float. If we try to convert an invalid string to a float, we will raise the ValueError: could not convert string to float.

To solve this error, ensure you strip the string of invalid characters like commas, spaces or brackets before passing it to the float() function.

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

ValueError: could not convert string to float 

In Python, a value is information stored within a particular object. You will encounter a ValueError in Python when you use a built-in operation or function that receives an argument with the right type but an inappropriate value.

A string is a suitable type to convert to a float. But several string values are not suitable to convert to float:

• A value that contains non-special terms, for example, ‘nan’ is a special term, “bread” is not.
• A value that contains a commas, speech marks and other non alphanumeric characters.
• A value that contains spaces.

We can convert inf and nan to floats because they represent specific floats in Python, namely infinity and NaN (Not a Number).

Example

Consider the following CSV file called money.csv that contains the epoch timestamp and money in two accounts.

"'1645916759'",20000,18000
"'1645916790'",21000,17000
"'1645916816'",20500,17250

Next, we will write a program that will read the information from the CSV file and print it to the console. We will import the csv library to read the CSV file. Let’s look at the code:

from datetime import datetime

with open("money.csv", "r") as money:

   readf = csv.reader(money)

   for line in readf:

       time = float(line[0])

       account_one = float(line[1])

       account_two = float(line[2])

       print(f'At date: {datetime.fromtimestamp(time)}, Account one value £{account_one}, Account two value £{account_two}')

We use the datetime library to convert the epoch timestamp to a date. Let’s run the code to see the result:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
      2     readf = csv.reader(money)
      3     for line in readf:
----≻ 4         time = float(line[0])
      5         account_one = float(line[1])
      6         account_two = float(line[2])
ValueError: could not convert string to float: "'1645916759'"

The error occurs because the epoch timestamp contains inverted commas, which are invalid string values to convert to a float.

Solution

We need to strip the epoch timestamp of the inverted commas using the String strip() method to solve this error. Let’s look at the revised code:

from datetime import datetime

with open("money.csv", "r") as money:

   readf = csv.reader(money)

   for line in readf:

       time = float(line[0].strip("'"))

       account_one = float(line[1])

       account_two = float(line[2])

       print(f'At date: {datetime.fromtimestamp(time)}, Account one value £{account_one}, Account two value £{account_two}')

Let’s run the code to see the result:

At date: 2022-02-26 23:05:59, Account one value £20000.0, Account two value £18000.0
At date: 2022-02-26 23:06:30, Account one value £21000.0, Account two value £17000.0
At date: 2022-02-26 23:06:56, Account one value £20500.0, Account two value £17250.0

The code successfully prints each line in the money.csv file.

Example #2

Let’s look at an example, where we write a program that converts a weight from kilograms to pounds. First, we will ask a user to insert the weight in kilograms that they want to convert to pounds:

weight = float(input("Enter the weight to convert to pounds: "))

Next, we will define the conversion value to convert kilograms to pounds:

convert_to_lbs = 2.205

Then, we will attempt to convert the kilogram value to pounds and print the result to the console.

weight_in_lbs = weight * convert_to_lbs

print(f'{weight}kg is {weight_in_lbs}lbs')

Let’s run the code to see what happens:

Enter the weight to convert to pounds: 87,50
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
----≻ 1 weight = float(input("Enter the weight to convert to pounds: "))
ValueError: could not convert string to float: '87,50'

We raise the ValueError because the string we input contains a comma.

Solution

To solve the error we can use a try-except block. The program will try to run the code in the “try” block, if unsuccessful, the program will run the code in the “except” block. Let’s look at the revised code:

convert_to_lbs = 2.205

try: 

    weight = float(input("Enter the weight to convert to pounds: "))

    weight_in_lbs = weight * convert_to_lbs

    print(f'{weight}kg is {round(weight_in_lbs,1)}lbs')

except:

    print('Please insert a valid weight. The weight cannot contain commas, spaces or special characters')

Let’s try the code and input an invalid string:

Enter the weight to convert to pounds: 87,50
Please insert a valid weight. The weight cannot contain commas, spaces or special characters

We see that the program executes the print statement in the except block. Let’s run the code and input a valid string:

Enter the weight to convert to pounds: 87.50
87.5kg is 192.9lbs

The code successfully executes the code in the try block and prints the kilogram and the converted pound value to the console.

Summary

Congratulations on reading to the end of this tutorial! The error ValueError: could not convert string to float occurs if you try to convert a string to a float that contains invalid characters. To solve this error, check the string for characters that you can remove and use the strip() method to get rid of them. If a value has a comma instead of a decimal point, you can use replace() to replace the comma.

You can also use a try-except statement to catch the ValueError and pass. This method is useful if you are taking input from a user.

For further reading on ValueErrors, go to the articles:

• How to Solve Python ValueError: list.remove(x) x not in list
• How to Solve Python ValueError: year is out of range

For further reading on converting values, go to the article: How to Solve Python TypeError: int() argument must be a string, a bytes-like object or a number, not ‘list’

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!

Pandas

The ValueError: could not convert string to float error occurs when you try to convert a string that does not contain a float number to a float. If the python string is not formatted as a floating point number, you could not convert string to float. The python ValueError: could not convert string to float will be thrown. The error is caused by a parsing error in the float() function with a string argument that cannot be parsed as a float number.

The float() function is used to convert a string with a float value to a float value. The float function parses the string and converts it as a float number. If an error occurs while converting a string to a float number, the python interpreter will throws this value error.

The string is supposed to have a valid float number. If the string is empty or does not contain a valid float number, the python interpreter can not convert it to a float number while parsing the string. In this case, the error “ValueError: could not convert string to float:” is thrown by the python interpreter.

Exception

The error “ValueError: could not convert string to float:” will be shown as below the stack trace.

Traceback (most recent call last):
  File "/Users/python/Desktop/test.py", line 1, in <module>
    print float('')
ValueError: could not convert string to float: 
[Finished in 0.0s with exit code 1]

Root Cause

The function float() is used to convert a string to a float number. The string is supposed to have a valid float number. If the string is either empty or does not have a valid float number, the python interpreter will throw an error while parsing the string. If the valid float value is passed to the string, this issue will be resolved.

Valid arguments in float() function

The following are the valid arguments for float() function. If you use one of the following, the error will not be thrown.

float() function with no argument – The default float() function which has no argument passed returns default value 0.0.

print float()    # returns 0.0

float() function with an integer value – If an integer value is passed as an argument in float() function, returns the float value.

print float(5)   # returns 5.0

float() functions with a string containing an integer value – If a string having an integer value is passed as an argument in float() function, returns the float value.

print float('5')   # returns 5.0

float() function with a float value – If a float value is passed as an argument in float() function, returns the float value.

print int(5.4)   # returns 5.4

float() functions with a string containing an float value – If a string having an float value is passed as an argument in float() function, returns the float value.

print float('5.4')   # returns 5.4

float() function with a boolean value – If a boolean value is passed as an argument in float() function, returns the float value for the boolean value.

print float(True)   # returns 1.0

Invalid arguments in float() function

float() function with an empty string – The empty string can not be parsed as an float value

print float('')     # throws ValueError: could not convert string to float:

float() function with a non-float string – If a string contains a non-float values such as characters and passed as an argument, the float() function will throw value error.

print float('q')     # throws ValueError: could not convert string to float: q

Solution 1

The string value should be checked whether it is a number or not using buid-in isnumeric() function. If a string contains a number, it is passed as an argument in the float() function. Otherwise, the user will be shown an error message.

Program

x='a'
print float(x)

Output

Traceback (most recent call last):
  File "/Users/python/Desktop/test.py", line 2, in <module>
    print float(x)
ValueError: could not convert string to float: a
[Finished in 0.0s with exit code 1]

Solution

x= u'a'
if x.isnumeric():
	print "float value is " , float(x)
else :
	print "Not a number"

Output

Not a number
[Finished in 0.1s]

Solution 2

If a string occasionally contains a non-numeric number, the build-in function isnumeric() is not a good option. In this case, try catch method will solve this issue. If the string contains an float number, it will be executed in the try block. Otherwise, an error message will be shown to the user in the error block.

Program

x='a'
print float(x)

Output

Traceback (most recent call last):
  File "/Users/python/Desktop/test.py", line 2, in <module>
    print float(x)
ValueError: could not convert string to float: a
[Finished in 0.0s with exit code 1]

Solution

x= u'a'
try:
	print ("float value is " , float(x))
except:
	print "Not a number"

Output

Not a number
[Finished in 0.1s]

In this Python tutorial, we will discuss how to fix an error, “Could not convert string to float Python“.

In python, to convert string to float in python we can use float() method. It can only convert the valid numerical value to a floating point value otherwise it will throw an error.

Example:

my_string = '1,400'
convert = float(my_string)
print(convert)

After writing the above code (could not convert string to float python), Ones you will print ” convert ” then the output will appear as a “ ValueError: could not convert string to float: ‘1,400’ ”.

Here, we get the error because the value is not valid and we used a comma. You can refer to the below screenshot could not convert string to float python.

To solve this ValueError: could not convert string to float we need to give the valid numerical value to convert my string to float by using float() method.

Example:

my_string = '23.8'
convert = float(my_string)
print(convert)

After writing the above code (could not convert string to float python), Ones you will print ” convert ” then the output will appear as a “ 23.8 ”. Here, the float() method converts the string to float. You can refer to the below screenshot could not convert string to float python.

This is how to fix could not convert string to float python.

Read: Python find substring in string

How to fix could not convert string to float python

Let us see how to fix could not convert string to float python

In this example, we got a ValueError because the function argument is of an inappropriate type. So, when we tried to typecast a string value it throws ValueError.

Example:

str = "Hi"
print(float(str))

The normal text is not supported by the float() function in python. You can refer to the below screenshot for the error.

To fix value error: could not convert string to float python, we have to give numeric text value to convert it successfully to float. we can use the below code to solve the above error.

Example:

str = "5.45"
print(float(str))

You can refer to the below screenshot to see the output for how to fix could not convert string to float python.

You may like the following Python tutorials:

• How to handle indexerror: string index out of range in Python
• How to convert an integer to string in python
• Slicing string in Python + Examples
• Convert string to float in Python

Here we checked how to fix error, could not convert string to float python.

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