[Solved] typeerror: type numpy.ndarray doesn’t define __round__ method

Have you ever found yourself tearing your hair out in frustration because of the “TypeError: type numpy.ndarray doesn’t define a round method” error while working with NumPy arrays in Python? Don’t worry! This error can be a real roadblock regarding getting your code up and running, but we’ve got your back. 

In this article, we’ll delve into the root causes of this pesky error, equip you with the tools to troubleshoot it like a pro, and reveal some slick alternatives to the round function to help you steer clear of this error in the future. 

Before we go into troubleshooting mode, check if you have installed NumPy correctly.

Now, let’s jump right in!

Understanding the Python Round function and its limitations

Python’s built-in round function will round a decimal value to the nearest integer. The first (required) input is the number that has to be rounded, and the second (optional) argument specifies how many digits after the decimal point the number should be rounded to.

The round function has many applications, but it also has several restrictions. One of its major drawbacks is the inability to round collections of values, such as lists, tuples, or NumPy arrays. Trying to round numbers in a NumPy array can lead to the “TypeError: type numpy.ndarray doesn’t define round method” problem.

Causes of the “TypeError: type numpy.ndarray doesn’t define round method” error.

Sure, here are five major causes of the “TypeError: type numpy.ndarray doesn’t define a round method” error with more detailed explanations:

1. Directly applying the round function to a NumPy array

 You can only use the round function on single values, not whole arrays or collections. If you attempt to round a NumPy array directly using the round function, Python will give you a “TypeError” because the array doesn’t have a defined round method.

2. Outdated or incompatible version of NumPy

 NumPy version 1.15.0 was the first to introduce the round function. If you try to use the round function in an older version of NumPy that doesn’t have it, you’ll get a “TypeError.”

3. Passing incompatible data types to the round function

 Only numeric data types can be accepted by the round function. Python will raise a “TypeError” if the function is passed non-numeric data types like strings or lists.

4. Missing or inconsistent values within the NumPy array

 The round function can behave unexpectedly if there are missing or inconsistent values within the NumPy array. If the array contains “NaN” or “Inf” values, the round function may return unexpected or erroneous results, resulting in the “TypeError.”

5. Outdated or incompatible version of Python

You can only use the round function in Python 3. x and newer versions. Using an outdated Python version will result in the round function not being recognized and a “TypeError” being thrown.

Exploring the shape and data types of NumPy arrays

1. Understanding NumPy Array Shape

Have you ever wondered how to determine the shape of a NumPy array in Python? Well, the `shape` attribute can help you out! An array’s shape tells you the array’s number of rows, columns, and dimensions. You can think of it as the “size” of the array. A one-dimensional array has only one axis, while a two-dimensional array has two axes, and so on.

To access the shape of an array, simply call the `shape` attribute on the array object. For example, `arr.shape` returns a tuple with the shape of the array `arr.` This tuple contains the number of elements in each dimension of the array. So, if you have a 2D array with shape (3, 4), it has 3 rows and 4 columns.

2. Accessing and Modifying NumPy Array Shape

What if you need to modify the form of an existing array? Numerous functions in NumPy facilitate this goal. ‘reshape’ is the most frequently used function since it allows you to alter the size of an array without affecting the information contained within it. When called with a new shape, the’reshape’ function creates a new array with that shape as its return value.

The ‘resize function is more appropriate if you want to make on-the-fly adjustments to the size of an existing array. The ‘resize method dynamically adjusts an array’s dimensions while already in use, populating any newly created slots with zeros. Remember that ‘resize’ changes the original array, so don’t lose any crucial information.

Ultimately, the ‘transpose’ function can switch the order of elements in an array. This function swaps the dimensions of the given array and returns the result as a new array. In the case of a two-dimensional array with dimensions (3, 4), the ‘arr.transpose()’ function would produce a new array with dimensions (4, 3).

3. Exploring NumPy Array Data Types

Integers, floats, booleans, and strings are data kinds that can be stored in a NumPy array. Each data type serves a different purpose and has its features. The ‘dtype’ attribute can be used to learn the data type of an array. The attribute’s string value indicates the array’s data type.

It’s vital to remember that the data types used by NumPy are distinct from those used by Python. NumPy’s ‘bool’ data type, for instance, is distinct from Python’s native ‘bool’ type. The precision of your computations may also be affected by the varying precision levels supported by the various NumPy data types.

4. Common Numeric Data Types in NumPy

NumPy supports various numeric data types, including integers and floats. Integers can be either signed or unsigned and can have different byte sizes. The most common integer types are `int8`, `int16`, `int32`, and `int64`. The byte size of an integer type determines the range of values it can hold.

Floats are used to represent decimal values and can also have different precision levels. The most common float types are `float16`, `float32`, and `float64`. The higher the precision level, the more accurate the calculations will be and the more memory the array will use.

To determine the byte size of a data type, you can use the `itemsize` attribute. This attribute returns the number of bytes needed to store an element of the data type.

5. Boolean and String Data Types in NumPy:

Boolean Data Types in NumPy

A boolean data type in NumPy is a data type that has only two possible values: True and False. Boolean arrays are created using comparison operators such as >, <, >=, <=, ==, !=, etc. When an element in the array satisfies the condition, the corresponding element in the boolean array is assigned the value True and False otherwise.

You can also mask and index with Boolean arrays. For example, boolean arrays can filter out some items in another array based on a boolean value. When working with big arrays, this is especially helpful when only a subset of the data that meets a given condition is required. Filtering away unwanted information from an array is another usage for Boolean arrays.

String Data Types in NumPy

NumPy’s string data type is used to store and retrieve text strings. Several different functions in NumPy, including numpy.array() and numpy.char.array(), can be used to generate string arrays. NumPy’s string data type also provides several useful text processing operations, such as identifying substrings, changing cases, and replacing text.

Text processing and modification are common applications of string arrays. For instance, string arrays can be used for textual data analysis and information extraction. String arrays can also be used to format text in a particular style or to extract relevant passages from a larger text.

Troubleshooting the Error by Checking the Data Types and Values in the Array

One common cause of this error is passing an array with incompatible data types or values to the round function. It means that the array may contain values that cannot be rounded, such as strings or booleans, or may have a data type incompatible with the round function.

To troubleshoot this error, it’s important to check the data types and values in the array before passing it to the round function. Here are two popular methods for troubleshooting the error.

Using the NumPy dtype attribute

One way to do this is by using the NumPy dtype attribute, which returns the data type of the array. For example, if you have an array named “arr,” you can check its data type using the following code:


It will print the data type of the array to the console, allowing you to ensure that it’s compatible with the round function.

In addition to checking the data type, you should also check the values in the array to ensure they are compatible with the round function. For example, if your array contains strings or booleans, you may need to convert them to a compatible data type, such as floats or integers, before passing them to the round function.

 Using the NumPy isnan function

Another way to troubleshoot this error is by using the NumPy isnan function to check for the array’s NaN (Not a Number) values. The round function cannot handle NaN values, so removing them is important before passing the array to the function. You can use the isnan function as follows:

import numpy as np

arr = np.array([1.0, 2.0, np.nan, 4.0])
arr = arr[~np.isnan(arr)]

This code creates an array with a NaN value and removes it using the logical not operator (~) and the isnan function. The resulting array can then be safely passed to the round function without encountering the “TypeError: type numpy.ndarray doesn’t define __round__ method” error.

Alternatives to the Round Function for Rounding Values in NumPy Arrays

If you’ve encountered the “TypeError: type numpy.ndarray doesn’t define a round method” error while working with NumPy arrays in Python, here we have some great alternative ways to round values for you.

1. numpy.around:

The numpy.around function rounds an array to a specific number of decimals. This method can round values in a NumPy array without getting a “TypeError” error. 

For example, if you have a NumPy array called “my_array” and want to round it to two decimal places, you can use the numpy.around function as follows:

import numpy as np

my_array = np.array([1.23456, 2.34567, 3.45678])
rounded_array = np.around(my_array, decimals=2)



[1.23 2.35 3.46]

2. numpy.ceil and numpy.floor:

The numpy.ceil and numpy.floor functions can round up or down to the nearest integer, respectively. These functions can also be used to round values in a NumPy array.

If you wish to round the value of a NumPy array named “my_array” to the nearest integer, you can do so with the help of the numpy.ceil function, as seen below.

import numpy as np

my_array = np.array([1.23456, 2.34567, 3.45678])
rounded_array = np.ceil(my_array)



[2. 3. 4.]

Similarly, if you want to round the values down to the nearest integer, you can use the numpy.floor function as follows:

import numpy as np

my_array = np.array([1.23456, 2.34567, 3.45678])
rounded_array = np.floor(my_array)



[1. 2. 3.]

3. numpy.trunc:

Third, numpy.trunc, which removes the decimal places from an array, returns only the integer values. Rounding values in a NumPy array is another possible usage for this function.

As an illustration, consider the following numpy.trunc example, in which a NumPy array named “my_array” has been reduced to two decimal places:

import numpy as np
my_array = np.array([1.23456, 2.34567, 3.45678])
rounded_array = np.trunc(my_array * 100) / 100



[1.23 2.34 3.45]

4. Custom rounding function:

Using the NumPy vectorize function, you can even design your unique rounding function. This function lets you design your rounding logic by applying a scalar function to each input array element.

The following is an example of a custom rounding function for a NumPy array that rounds each value to the nearest multiple of 0.5.

import numpy as np

def my_round(x):
    return np.round(x * 2) / 2

my_array = np.array([1.23456, 2.34567, 3.45678])
rounded_array = np.vectorize(my_round)(my_array)



[1.  2.5 3.5]

Best Practices to Avoid the “TypeError: type numpy.ndarray doesn’t define round method” Error

While the “TypeError: type numpy.ndarray doesn’t define round method” error can be frustrating, there are some best practices you can follow to avoid encountering it in your code.

1. Specify the Data Type of Your NumPy Arrays Explicitly

When a mathematical operation or function is attempted on an array of unknown or unspecified data type, the “TypeError: type numpy.ndarray doesn’t define round method” error occurs. To prevent this, you should always use the ‘dtype’ argument to define the data type of your arrays. For example:

import numpy as np

# Create an array with a specified data type
arr = np.array([1.5, 2.5, 3.5], dtype=np.float32)

# Round the values in the array using numpy.around
arr_rounded = np.around(arr)


Here we’ve created a NumPy array with the data type `np.float32`, which tells Python that the array should contain 32-bit floating-point numbers. By specifying the data type explicitly, we can ensure that the array is compatible with the `np.around` function and other mathematical operations we might want to perform.

2. Double-Check the Shape and Dimensions of Your Arrays

Another common cause of the “TypeError: type numpy.ndarray doesn’t define a round method” error is trying to operate on an array with an incompatible shape or dimensionality. For example, if you try to round a two-dimensional array using the `round` function, you’ll likely encounter this error:

import numpy as np

# Create a 2D array
arr = np.array([[1.5, 2.5], [3.5, 4.5]])

# Try to round the values in the array using the round function
arr_rounded = round(arr)


Verifying the array’s dimensions and shape before performing any operations will help you prevent this problem. NumPy arrays have ‘shape’ and ‘dtype’ attributes that can be used to determine their dimensions and data type, respectively. If you’re stuck deciding on an appropriate array shape or size, it’s best to contact the NumPy documentation or a seasoned Python programmer.

4. Keep your code organized

Errors can be reduced, and problems can be resolved more quickly by using clear and simple code to read. Make your variable names descriptive, divide your code into functions, and comment on it to clarify its purpose.

5. Use vectorized operations:

Use vectorized operations, which are supported by NumPy arrays and are oftentimes significantly faster and more efficient than applying operations element by element. Using vectorized operations can also avoid errors from incompatible data types or dimensions.

6. Use Alternative Methods for Rounding Values in NumPy Arrays

If you want to avoid the “TypeError: type numpy.ndarray doesn’t define round method” error altogether, you can use the alternative methods mentioned above for rounding values in NumPy arrays. 

Let’s Wrap It Up

Errors like “TypeError: type numpy.ndarray doesn’t define a round method” are a common stumbling block for newcomers to NumPy programming. However, this issue can be fixed and avoided with a deeper knowledge of the structure and data types of NumPy arrays and the many methods available for rounding values. 

To avoid unexpected errors, you should always verify your arrays’ data types and values. These guidelines will make your NumPy code readable, efficient, and error-free.

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