Convert String to Double in Python| 3 Methods Explained

Are you curious to know “How To Convert String To Double in Python?” In Python, when a programmer takes input using the built-in `input()` function, the input is captured as a string. This means that regardless of the value user enters (whether it’s a number, text, or any other value), Python treats it as a sequence of characters, represented by a string. As Python is a dynamically typed language it means data types of variables are not declared beforehand and Python will not know what the user will enter. Hence, it represents the input as a collection of characters. Here’s a simple example to illustrate the type of user input  

Code to illustrate the type of user input:

 

# Taking user input
message = input("Please enter a message: ")
pincode = input("Please enter the recipient pincode: ")

# Displaying the captured input
print("Message:", message , " " , type(message))
print("Pincode:", pincode, " ", type(pincode))

Output

Please enter a message: Hello Buddy, In for a football game coming Saturday?!
Please enter the recipient pincode: 59864

Message: Hello Buddy, In for a football game coming Saturday?! <class 'str'> 

Pincode: 59864 <class 'str'>

From the output, we can see despite varied data types, both user input of the message and pin code is received as a string.

What Are The Methods To Convert String to Double in Python? Read Below

 

1. Using float() Function

  The most straightforward method is to use the built-in float() function, which converts a string to a floating-point number. It represents numbers in base-2 format. float() has a fixed number of bits allocated for the mantissa (fractional part) and the exponent in the binary representation.

# _pi is currently a String
_pi = "3.14159265359"
value = float(_pi)
print(" Type of Pi" , value , " ", type(value))

if you are facing any issues in understanding the code, then you can always get professional Python assistance from experts online. This will not only help you in overcoming challenges in understanding but also excel in your Python assignments. Output:

Type of Pi 3.14159265359 <class 'float'>

Diverse Illustrations for String to Float Conversion

Converting strings to double (floating-point) values in Python:

# Converting strings to double (floating-point) values in Python
# Example 1: Convert a positive decimal string to a double
print(float('+1.23'))
# Example 2: Convert a negative integer string with leading whitespace to a double
print(float('-99887\n'))
# Example 3: Convert a positive string in exponential notation to a double
print(float('+5.7E6')) 

# Example 4: Convert a special string to a double (Negative Infinity)
print(float('-Infinity'))

Also, if you’re interested to know about different methods associated with splitting a string in C++, then you can read out our article. Output:

1.23
-99887.0
5700000.0
-inf

One thing to note is that if the string to be converted is not a valid floating-point number, a ValueError will be raised. You should handle this exception if necessary.  

2. Using Decimal Module

  Decimal Module provides precise decimal representation without rounding errors. It represents numbers in base-10 format.

from decimal import Decimal
value_str = "3.14159"
value = Decimal(value_str)
print(value, " " , type(value))

Output:

3.14159 <class 'decimal.Decimal'>

Precision and Rounding

The decimal module allows you to specify the desired precision when performing arithmetic operations.

from decimal import Decimal, getcontext
getcontext().prec = 10 # Set precision to 10 decimal places
value_pi = "3.14159265359 "
value = Decimal(value_pi)
print(value)

Output:

3.1415926535

3. Using numpy Library:

NumPy library is mostly used when performing tasks on machine learning as it has more advanced numerical functions. NumPy float() has numpy.float64 data type.

import numpy as np
golden_ratio = "1.61803398875"
phi = np.float64(golden_ratio)
print(phi, " ", type(phi))

Output:

 1.61803398875 <class 'numpy.float64'>

What Are The Varied scenarios where you might need to convert a string to a double?

 

1.File I/O :

When parsing data from files, the data is often read as strings. If the file contains numeric values that you need to use for calculations, you would need to convert those strings to doubles before performing the calculations.

2. API Responses:

When working with APIs that provide data in string format, you might need to convert the string data to doubles to process it correctly.

3. Command-Line Arguments:

When a script or program accepts command-line arguments, these arguments are typically received as strings. If the arguments are supposed to be numeric values, you’d need to convert them to doubles.

Conclusion:

Converting strings to double (floating-point) values in Python is necessary when handling user inputs or working with numeric data. These techniques discussed differ based on specific use cases. The primary method discussed involved a built-in `float()` function, which readily converts a string representation of a number to a floating-point value. However, for large floating numbers, it might give incorrect round-off values. For situations very precision is important, the Decimal module comes in handy. Furthermore, NumPy offers more advanced features to work on floats and doubles. To clear the concept of float and double, you should first know the differences between them.