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Converting Between Numeric Types in Python: A Comprehensive How-To Guide

Updated: at 02:01 AM

In Python, dealing with different numeric types is very common. You may need to convert an integer to a floating point number, a float to a string representation, or vice versa. Converting between numeric types in Python is straightforward, but it helps to understand the differences between integers, floats, complex numbers, and other numeric objects in Python to avoid errors and unintended results.

This comprehensive guide will provide a deep dive into converting between the main numeric types in Python. We will cover:

Table of Contents

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Overview of Major Numeric Types in Python

Python contains many numeric data types to represent numbers. The main types include:

These types serve different purposes and have tradeoffs in terms of precision, range, memory usage and numeric behavior. Understanding those tradeoffs helps inform when and how to convert between types in Python.

Explicit vs Implicit Type Conversion

Python allows flexible intermixing of numeric types thanks to implicit and explicit conversion between types.

Implicit Type Conversion

Python will automatically coerce numeric types as needed in mixed type expressions. This is implicit type conversion:

>>> 5 + 4.3 # int + float -> float

>>> 3 * True # int * bool -> int

>>> 4j + 2 # complex + int -> complex

Python tries to convert types to avoid errors and allow reasonable mixed-type math to work. Some key rules:

Danger: Implicit conversion can lead to strange bugs! Be careful mixing types.

Explicit Type Conversion

You can control conversion more explicitly by casting values using type constructors:

>>> int(5.4)

>>> float(5)

>>> str(5.1)

Casting with constructors makes the conversion explicit and visible.

Explicit casting also allows control over things like rounding behavior and formatting.

Converting Between int, float, and complex

The int, float and complex numeric types have particular conversion behaviors in Python due to their math properties.

int to float

Converting an integer to floating point is intuitive - simply change to a decimal form:

>>> float(5)

>>> float(-10)

All math on a float retains decimal precision, even for integers:

>>> 5 / 2

>>> float(5) / 2

float to int

Casting a float to integer rounds down to the nearest whole number, truncating the decimal:

>>> int(5.7)

>>> int(4.2)

>>> int(-3.8)

This can cause loss of data, so be careful!

Complex Conversion

Complex numbers contain real and imaginary float parts. Convert real numbers to complex with 0j imaginary part:

>>> complex(5)

>>> complex(4.2)

Create a complex number by passing real and imaginary parts:

>>> complex(2.1, -3.5)

Access the parts with .real and .imag attributes:

>>> c = complex(2.5, 3)
>>> c.real
>>> c.imag

Changing Numeric Precision and Range

Different numeric types have tradeoffs in precision vs range. You can use type conversion to change precision or range as needed.

float to int: Losing Precision

Floats have decimal fraction precision, but may lose precision when cast to integers:

>>> float(1.99999999)

>>> int(1.99999999)
1 # Precision lost!

Only use float → int when you don’t need the fractional precision.

int to float: Gaining Precision

Integers have unlimited range, but converting to float provides fractional precision:

>>> 2000000000000

>>> float(2000000000000)
2e+12 # Float has precision

Use float for scientific domains even with very large numbers.

float to Fraction: Precise Rationals

The fractions.Fraction type keeps numerator and denominator instead of a floating point value. This avoids cumulative rounding errors:

>>> from fractions import Fraction
>>> Fraction(1.1)
Fraction(2476979795053773, 2251799813685248) # Precise value

Fractions are useful when float rounding causes issues like equality testing:

>>> .1 + .1 + .1 == .3 # False due to float rounding!

>>> Fraction(1, 10) + Fraction(1, 10) + Fraction(1, 10) == Fraction(3, 10)

float to Decimal: Controlling Precision

Python’s decimal.Decimal type allows control of rounding and number of decimal places:

>>> from decimal import Decimal
>>> Decimal(.1)

>>> Decimal(.1).quantize(Decimal('0.000')) # Round to 3 decimals

Decimals are great for things like financial applications.

Best Practices for Numeric Conversion

Here are some tips for safely and effectively converting between numeric types in Python:

Following best practices helps avoid weird errors and numeric issues down the line!

Real World Example - Data Science Calculations

As a data science example, let’s look at calculating summary statistics on a dataset. We’ll see where numeric type conversions are required and how to implement them properly.

First, we need to read in the raw data. The numbers are stored as strings by default:

import pandas as pd

data = pd.read_csv('dataset.csv')
print(data['value'].dtype) # 'object' (string)

To find quantitative insights, we need to convert the strings to numbers. Let’s convert to floats:

values = data['value'].astype(float) # Convert column to floats

Now we can calculate statistics like the mean, standard deviation, and variance:

mean = values.mean() # Get float mean
stdev = values.std() # Get float standard deviation
variance = stdev ** 2 # Get float variance

But if we try to print these floats, we run into rounding issues:

# 2.3472971124764283 - Ugly rounding!

To nicely print the results, we’ll convert the floats to rounded decimals:

from decimal import Decimal

# 2.35 - Rounded to 2 decimals

The correct numeric types allow both precision for math and nice presentation of results!


This guide covered the key details of converting between numeric data types in Python:

Understanding numeric conversion in Python helps you effectively work with the myriad of available numeric types for your programming needs. Both simple and advanced mathematical applications require knowing how to properly convert integers, floats, decimals, and more. Master these concepts to become proficient in handling numbers in Python!