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# Python a += b is not always a = a + b

If two variables are of the same data types and not iterators like list and dictionary etc, then the expressions a += b is same as a =+b gives the same result. But when n iterator is involved we can not always expect the same. Below is one of such scenario.

## Case of a = a +b

Here we can see when we apply the expression to a list and a string expecting they will get merged, we get back an error.

### Example

x ='Hello ' z_list = [1,2,3] z_list = z_list + x print(z_list)

### Output

Running the above code gives us the following result −

Traceback (most recent call last): File "C:\Users\Pradeep\AppData\Roaming\JetBrains\PyCharmCE2020.3\scratches\scratch.py", line 11, in z_list = z_list + x TypeError: can only concatenate list (not "str") to list

## Case of a += b

But when we apply the expression a += b we see that the sting implicitly gets converted to series of elemnst to become a part of the list.

### Example

z_list = [1,2,3] x ='Hello' z_list += x print(z_list)

### Output

Running the above code gives us the following result −

[1, 2, 3, 'H', 'e', 'l', 'l', 'o']

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