Python float() Function

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The float() function is used to convert a given number or string into a floating-point number.

float() Syntax

The syntax for float() is:


float() Parameters

The float() method takes a single parameter:

x: (Optional) The value you want to convert to a floating-point number.

float() Return Value

The float() method returns:

  • Equivalent floating point number if an argument is passed
  • 0.0 if no arguments passed
  • OverflowError exception if the argument is outside the range of Python float

Converting from Different Data Types

Conversion from Integer to Float

Converting an integer to a floating-point number essentially means representing the integer with a decimal point.

Using the float( ) function

The float() function provides a straightforward way to convert an integer into a floating-point number. When an integer is passed as an argument to the float() function, the returned value is a floating-point representation of that integer.


integer_number = 7
floating_point = float(integer_number)

print(floating_point)  # Outputs: 7.0

In the above example, the integer 7 is converted to the floating-point number 7.0.

Why Convert Integers to Floats?

There are several scenarios where such a conversion might be necessary:

Mixed-Type Arithmetic: In mathematical operations involving both integers and floats, it’s often convenient to have all operands in the same data type, especially if the expected output is a float.

result = 3 + 2.5  # The integer 3 will be implicitly converted to a float
print(result)  #output - 5.5

Function Requirements: Some functions or methods, especially in various libraries or frameworks, might require floating-point inputs even if the value is a whole number.

Precision and Division: If you want to ensure that division between integers produces a floating-point result (in Python 3.x, this is the default behavior), you might convert integers to floats first.

result = float(5) / float(2)  # Outputs: 2.5

Data Representation: In certain contexts, it might be clearer to represent all numbers, including whole numbers, as floating-point numbers, especially if they’re part of a larger set of data that includes non-whole numbers.

Conversion from String to Float

The float() function can be used to convert strings that represent valid floating-point numbers (or integers) into actual float data types.

Basic Usage:

string_num = "123.456"
converted_float = float(string_num)
print(converted_float)  # Outputs: 123.456

In the example above, the string "123.456" is converted to the float number 123.456.

Important Points:

Valid Number Format: The string should be in a format that represents a valid number. This means it should possibly start with a sign (+ or -), followed by digits, and can contain a decimal point.

valid_string = "-123.45"
print(float(valid_string))  # Outputs: -123.45

Exceptions: If the string is not in a format that represents a valid floating-point number, using float() will raise a ValueError.

invalid_string = "123abc"
# This will raise an error: ValueError: could not convert string to float: '123abc'

Whitespace: Leading and trailing whitespaces in the string are ignored during the conversion. However, whitespaces in the middle of the number will cause a ValueError.

valid_with_whitespace = "   123.45   "
print(float(valid_with_whitespace))  # Outputs: 123.45

Special Values: Strings representing special float values like “inf”, “-inf”, and “NaN” (Not a Number) can also be converted.

print(float("inf"))   # Outputs: inf
print(float("-inf"))  # Outputs: -inf
print(float("NaN"))   # Outputs: nan

Practical Applications:

User Input: When collecting user input using the input() function, the data is returned as a string. If you expect the user to enter a number, you might need to convert this string to a float.

user_input = input("Enter a number: ")
number = float(user_input)

Data Parsing: When reading data from files, databases, or APIs, numeric values are often presented as strings. Converting these to floats is essential for further numerical processing.

Conversion from Boolean to Float

Booleans can be directly converted into numeric types in Python, both integers and floats. This ability is rooted in the binary nature of Boolean values, where True corresponds to 1 and False corresponds to 0.

Using the float() function, Booleans can be easily converted to floating-point numbers:

  • True converts to 1.0
  • False converts to 0.0

Basic Usage:

print(float(True))  # Outputs: 1.0
print(float(False)) # Outputs: 0.0

Practical Implications:

Arithmetic Operations: The numeric mapping of Booleans allows for their direct use in arithmetic operations.

result = True + 4.5   # This will give 5.5 because True is treated as 1.0

Logical Operations: Sometimes, in logical expressions, it’s useful to compute the sum of Booleans. For instance, to count how many conditions are True.

conditions = [True, False, True, True]
count_true = sum(map(float, conditions))
print(count_true)  # Outputs: 3.0

Data Type Conversion: In some data processing tasks, especially when working with certain libraries or datasets, it might be necessary to convert Booleans to numeric types for consistency or computation.

Handling Exceptions and Edge Cases

The float() function can raise exceptions in certain situations:


This occurs when you pass a string that’s not a valid number.

# This will raise an error


This occurs when you pass a data type that cannot be converted to float, like a list or dictionary.

# This will raise an error

Limitations and Precision of Floats

Floating-point numbers in Python (and in most programming languages) have precision limitations. Due to their binary representation, some decimal numbers cannot be represented exactly. This can lead to potential rounding errors.

For instance:

print(0.1 + 0.2)  # Might not output 0.3 exactly, but something like 0.30000000000000004

When performing operations that require high precision, consider using the decimal module in Python.


The float() function in Python, though seemingly straightforward, carries nuances that developers should be aware of. Understanding its behavior, especially regarding precision and type conversion, can save you from potential pitfalls in your coding journey. Whether you’re building simple scripts or complex applications, having a firm grasp of how to handle floating-point numbers will undoubtedly serve you well.

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