How to Fix TypeError: Must Be Real Number, Not STR

The TypeError: must be real number, not str error involves using a wrong type and a non-real number, and in this case, an str type.

Working with datatypes can be tricky, but it is important to enforce or ensure you are parsing the right data type to a function to avoid such TypeError.

This article will explain how the TypeError: must be real number, not str error occurs in the first place and how to solve it using type conversion.

Use float() or int() to Solve TypeError: must be real number, not str in Python

When working with functions, especially built-in functions, the arguments required are often of a particular type. It could be any of the primitive data types, int, float, string, or Boolean.

Therefore, it is important to make sure that the values we are working with and parsing are of the right data.

A typical example is working with the built-in input() function to take a number and work with the number in a simple mathematical expression.

number = input("Enter a Number: ")
print(number / 34 + 45 * number)

Output:

Enter a Number: 12
Traceback (most recent call last):
  File "C:\Users\akinl\Documents\Python\steps.py", line 2, in <module>
    print(number/34 + 45 * number)
TypeError: unsupported operand type(s) for /: 'str' and 'int'

Here, we have a TypeError message because the number binding held a string data 12; instead of an integer or float number, 12.

However, this TypeError: unsupported operand type(s) for /: 'str' and 'int' is different from this TypeError: must be real number, not str error. The distinction is in the operation that’s happening.

Let’s use the math library in Python to round down the number that the user inputs.

import math

number = input("Enter a Number: ")
print(math.floor(number))

Output:

Enter a Number: 12.45
Traceback (most recent call last):
  File "C:\Users\akinl\Documents\Python\steps.py", line 3, in <module>
    print(math.floor(number))
TypeError: must be real number, not str

Now, the TypeError is different because we are parsing the number binding, which contains a string to the floor() method, and the method requires a number, float or integer.

Therefore, to solve the problem, we need to convert the datatype of the value the user passes to the number binding to float or integer, depending on what we need.

The built-in float() function is most appropriate when dealing with floating point numbers. Given that we need decimal numbers to round up, we need the float() function.

import math

number = float(input("Enter a Number: "))
print(math.floor(number))

Output:

Enter a Number: 123.45
123

The int() function can be useful for cases where the number needed is a whole number. If we only need whole numbers to be parsed to the sin() method, we can use the int() method.

import math

number = int(input("Enter a Number: "))
print(math.sin(number))

Output:

Enter a Number: 12
-0.5365729180004349

It can be easier to solve for simpler cases but trickier for some complex or harder scenarios. For example, it might be hard to see where you need to convert if you are working on a randomized trigonometric calculator.

It is always better to convert immediately, especially before the operation expression. In this case, the mathematical operation.

import random
import math


def create():
    global sideA
    sideA = format(random.uniform(1, 100), ".0f")
    global sideB
    sideB = format(random.uniform(1, 100), ".0f")
    global angleA
    angleA = format(random.uniform(1, 180), ",.3f")
    global angleB
    angleB = ANGLE_B()

    return angleB


def ANGLE_B():
    angle = format(math.asin(sideB * (math.sin(angleA) / sideA)), ".3f")
    return angle


print(create())

Output:

Traceback (most recent call last):
  File "c:\Users\akinl\Documents\Python\float.py", line 18, in <module>
    print(create())
  File "c:\Users\akinl\Documents\Python\float.py", line 11, in create
    angle_b = ANGLE_B()
  File "c:\Users\akinl\Documents\Python\float.py", line 15, in ANGLE_B
    ang = format(math.asin(side_b*(math.sin(angle_a)/side_a)), '.3f')
TypeError: must be real number, not str

If you trace the error you can see it starts from print(create()) which calls the ANGLE_B() function uses the binding sideA, sideB, and angleA.

These bindings are parsed to the math methods, which require float and int data values. However, the binding’s datatype is strings and needs to be converted to either float or int.

In this case, the more responsible way to solve the code issue is to convert the datatype before use in mathematical expression since we don’t need to change the value again.

import random
import math


def create():
    global sideA
    sideA = float(format(random.uniform(1, 100), ".0f"))
    global sideB
    sideB = float(format(random.uniform(1, 100), ".0f"))
    global angleA
    angleA = float(format(random.uniform(1, 180), ",.3f"))
    global angleB
    angleB = ANGLE_B()

    return angleB


def ANGLE_B():
    angle = math.asin(sideB * (math.sin(angleA) / sideA))
    return angle


print(create())

Output:

0.7293575839721542

Therefore, be defensive when dealing with datatypes, and make sure that after working with the date, convert the data to the necessary datatype.