How To Convert String To Float In Python

Type conversion is used to convert one data type to another data type. In Python, there are two ways to do the conversion, Implicit and Explicit. In implicit type conversion, it takes place during compilation or runtime. It is also known as automatic type conversion which a Python interpreter performs.

In explicit type conversion, inbuilt functions are used by the user or programmer. It is also called type casting or manual conversion.

As we know that strings are a sequence of characters that are enclosed within single or double quotes. (‘ ’ or “ ”). Also, they are immutable, so we can’t change them once they are declared.

Float is one of the data types of python programming used to represent a floating-point number. Float is always written with decimal points by dividing the integer and fractional parts.

Why is there a need to convert strings to float in Python

Here are the reasons why the string to float conversion is required:

• Sometimes, while working with Python data, we can have a problem in which we need to perform a conversion of one data type to another data type.
• In Python, there are many situations where it is necessary to convert a string to a float data type. This is because Python is a dynamically typed language, which means that the data type of a variable can change during the execution of a program.
• One common situation where string-to-float conversion is required is when dealing with user input.
• User input is typically in the form of a string, and if the input is expected to be a number, it must be converted to a float before it can be used in calculations.
• Another situation where string-to-float conversion is useful is when reading data from a file or a database. Data read from these sources is often in string format, and if it needs to be used in calculations, it must be converted to a float.
• It helps us do operations on values having different data types.

Ways to convert string to float in Python

There are several approaches to converting string to float in Python.

1. Using float function
2. Converting a string with commas to float
3. Converting a list of string to float
4. Converting using numpy
5. Converting string to specified decimal points
6. Converting the string to a float list

Approach 1: Using Float function

This method converts a simple string into floating point numbers using the float method within the program. This method only accepts one parameter. If we do not pass any argument, then the method returns 0.0.

Here is an example of using float() method to convert string into float.

Code:

x = '3.14'  
a = float(x)  
print("The float value is ",a)

Output:

>>> 
The float value is  3.14

Code Explanation:

1. In this example, first, we declare the string value that would be converted into a float value.
2. After this use of float() function converts into float value and is stored into a new variable.
3. Finally, after executing the program, we can observe the desired output.

Approach 2: Converting string with commas to float

In this method the string contains the number and also has an extra comma. Therefore, converting this kind of string into floating point numbers is a little hard. If you are trying to convert such a string directly with the use of the float method it will raise an error.

So, here will use the replace() method to remove all commas from the string before passing it into the float function.

Here is an example of string with commas

Code:

a = '25,.80'  
ans = float(a.replace(',', ''))  
print("The float value is ",ans)

Output:

The float value is  25.8

Code Explanation:

1. In this example, we declare string value that would be converted into floating point value, also comma is present before the decimal point.
2. After this statement use the replace method within the float function.
3. Finally, after executing the program, we can observe the desired output.

Approach 3: Converting a list of strings to float

In this approach, a list containing all elements as strings in it. To convert a list of strings into floating-point numbers you have to use a loop to iterate throughout the list.

Here is an example of a list of string-to-float values.

Code:

a=['1.25', '2.25', '3.25', '9.25', '5.25']  
list1=[]  
for i in a:  
  list1.append(float(i))  
print('The list of float values:',list1) 

Output:

The list of float values: [1.25, 2.25, 3.25, 9.25, 5.25]

Code Explanation:

1. In this program, we declare the list that contains all string values as its elements. After this, we create an empty list.
2. In this program, use a for loop for taking each element and converting them into a float, and storing them into list1.
3. After execution of the program, we get desired output.

Approach 4: Converting using numpy

NumPy is a library for the Python programming language, adding support for large, multi-dimensional arrays and matrices, along with a large collection of high-level mathematical functions to operate on these arrays. If we want to use the NumPy library in the code firstly we have to import it using import numpy as np. Later, we will use the astype() method to convert a string into a float in python.

Code:

import numpy as np 

a=np.array(['0.25', '9.34', '3.02', '10.22', '5.43']) 

ans=a.astype(float) 

print('The list having float values:',ans)

Output:

The list having float values: [ 0.25  9.34  3.02 10.22  5.43]

Code Explanation:

1. In this program, first we have to import numpy libraries.
2. After that, we declare one array that has all string values.
3. After this step, the next step is to use astype() and specify float in it since this is the functionality or feature we wish to apply on all the elements.
4. After execution of the program, we get the required output.

Approach 5: Converting string to the specified decimal point

Floating point values often need more precision for the number of zeros after the decimal point.

In such a scenario, we can use the float() method for conversion from a string to a float value and then use the format() method to specify the number of decimal places for the float value.

The below syntax has been used for this method.

“{:.Nf}”.format( float value), where N indicates the number of decimal points you wish to put. According to that number, the floating number will be rounded.

In the below code of conversion of string to the specified decimal point.

Code:

a='5.88656' 

val=float(a) 

ans="{:.3f}".format(val) 

print(ans)

Output:

5.887

Code Explanation:

1. In the above code, firstly we declare one variable that stores string value that we would like to convert into a float value.
2. After that statement, will use the float method and pass the variable a.
3. In our output, we want three decimal places, that part mentioned in this statement.
4. After execution of the code, we get our desired output.

Approach 6: Converting the string to a float list

In this method, we need to initialize the string, later we will use the float() method and split() method for converting a string into floating-point numbers.

The below code shows the conversion of string to float list

Code:

a='2.23, 3.44, 3.82, 7.89, 7.43' 

ans=[float(i) for i in a.split(', ')] 

print("The list having float values: "+str(ans))

Output:

The list having float values: [2.23, 3.44, 3.82, 7.89, 7.43]

Code Explanation:

1. In the above code, firstly we declare the string that we would like to convert into a float list. Here, a variable stores the different decimal values separated by commas.
2. After that statement, we will make use of list comprehension that will take each value and convert it into the required type.
3. After the successful execution of the code will get the required output.

Best approaches for converting a string into float:

The float() method converts any data type into a floating-point number. This method accepts only a single parameter. These are the best approaches for converting a string into float point numbers in Python due to the following reasons.

• Simplicity: float(x) method is a built-in function of python that is easy to use for the conversion of one data type to another. Because the Python language itself has inbuilt libraries and functions that are easily converted from string to float.

• Built-in support for primitive and non-primitive data types: The float() method supports both primitive and non-primitive data types.

Sometimes, in Python, we require the collection of values to be converted into another data type rather than a single value. At that time implicit method or explicit method will be used.

Sample Problems for Converting String to Float in Python

Sample Problem 1:

Suppose you want to write a Python program that calculates the average of four numbers inputted by the user.

Solution:

1. In this example, the input function is used to get four numbers as strings from the user.
2. After that, each of these strings is converted to a float using the float function.
3. Finally, the average of four numbers is calculated.

Code:

num1 = input("Enter the first number: ") num2 = input("Enter the second number: ") num3 = input("Enter the third number: ") num4 = input("Enter the fourth number: ") # Convert the string inputs to float num1 = float(num1) num2 = float(num2) num3 = float(num3) num4 = float(num4) # Calculate the average avg = (num1 + num2 + num3 + num4) / 4   print("The average of the three numbers is:", avg)

Output:

Enter the first number: 20

Enter the second number: 32

Enter the third number: 35

Enter the fourth number: 45

The average of the three numbers is: 33.0

Sample Problem 2:

How do you convert a string variable into a float which prints its datatype with value?

Solution:

1. In the code, we first initialize a string variable “str_variable” with the value “8.96”.
2. After that statement, use of float function that would be converted the string value into a float value.
3. Finally, it prints the result with its datatype.

Code:

# Initialize a string variable
str_variable = "8.96"

# Convert the string variable to a float
float_variable = float(str_variable)

# Print the data type and value of the float variable
print("The data type of float_variable is:", type(float_variable))
print("The value of float_variable is:", float_variable)

Output:

The data type of float_variable is: <class 'float'>
The value of float_variable is: 8.96

Sample Problem 3:

How do you calculate the average price of products, if you have a comma-separated string of numbers representing the price of that product?

Solution:

1. In this example, we start with a comma-separated string of prices (prices_str). We use the split() function to split the string into a list of strings (prices_list) using the comma as the delimiter.
2. Then, we loop through each string in the list, converting it to a float using the float() function and appending the resulting float to a new list(prices_float)
3. Finally, we calculate the average of the prices by summing the floats in the prices_float list.

Code:

prices_str = "11.99, 9.75, 12.50, 10.99"

# Split the string into a list of strings
prices_list = prices_str.split(",")

# Convert each string to a float and store it in a new list
prices_float = []
for price in prices_list:
    price_float = float(price)
    prices_float.append(price_float)

# Calculate the average of the prices
avg_price = sum(prices_float) / len(prices_float)

print("The average price is:", avg_price)

Output:

The average price is: 11.307500000000001

Sample Problem 4:

Suppose you have a list of strings, and  you want to convert that list into a list of floats in Python?

Solution:

1. In this solution, the first statement specifies a variable that stores a list of strings. After that create one empty list as listfloats.
2. In the next statement use a for loop to iterate throughout the list.
3. After that statement will use the append function which appends the converted item into the new list

Code:

str = ['1.6', '2.9', '3.78', '5.4']
listfloats = []
for item in str:
    listfloats.append(float(item))
print(listfloats)

Output:

[1.6, 2.9, 3.78, 5.4]

Sample Problem 5:

How to convert list of string to a NumPy array of floats in Python?

Solution:

1. In this example, firstly we need to import numpy as np.
2. In the next statement astype was used. It is a NumPy function that converts the string to a float.
3. Finally we get the desired output.

Code:

import numpy as np
string_array = np.array(["17.562", "12.36", "22.23", "100.23"])
float_array = string_array.astype(float)
print(float_array)

Output:

[ 17.562  12.36   22.23  100.23 ]

Sample Problem 6:

Suppose that you have a string and you want to desire output with three decimal places.

Solution:

1. First, in the above code, we first declare one variable that stores a string value that we would like to convert into a float value.
2. After that statement, we will use the float method and pass the variable a.
3. In our output, we want three decimal places, that part mentioned in this statement.
4. After execution of the code, we get our desired output

Code:

a='5.88456'  
val=float(a)  
ans="{:.3f}".format(val)  
print(ans)

Output:

5.885

Conclusion

In this article, details of python string and float values are given with explicit methods used to convert a string into float values. While programming, there are many situations where we have to convert from one type to another data type.  Here, we use an explicit method to convert one data type to another data type.