University of Michigan - Ann Arbor

A semantic error, also known as a logic error, occurs when a program runs successfully without any errors, but the outcome of the code is not what the programmer had intended. 

Semantic Errors

https://runestone.academy/runestone/books/published/fopp/index.html

Runestone: Foundations of Python Programming

Which of the following is a semantic error?

The problem with semantic errors in Python is that the program you wrote is not the program you wanted to write. The meaning of the program (its semantics) is wrong. Identifying semantic errors can be tricky because it requires you to work backward by looking at the output of the program and trying to figure out what it is doing.

Why Semantic Errors are Hard to Identify

- String concatenation instead of arithmetic addition
```
num1 = input('Enter a number:')
num2 = input('Enter another number:')
sum = num1+num2
print('The sum of', num1, 'and', num2, 'is', sum)
```
This program runs and produces a result, but it is not the result intended. This is because the program contains a semantic (logic) error. The error is that the program performs string concatenation instead of integer addition. To solve this, the program must perform the necessary integer conversions before calculating the sum.

Fix:
```
sum = int(num1)+int(num2)
```

- Order of operations
```
x = int(input('Enter a number'))
y = float(input('Enter a number'))
z = x+y/2
print('Average:', z)
```
This program runs and produces a result, but it is not the result intended. This is because the program contains an error in arithmetic order of operations. 

Fix: 
```
z = (x+y)/2
```

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