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

 Live Demo

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']

Pradeep Elance

Published on 25-Jan-2021 07:38:08

• Related Questions & Answers
• Find FIRST & FOLLOW for the following Grammar.\nS → A a A | B b B\nA → b B\nB → ε
• Larger of a^b or b^a in C++
• Show that the following grammar is LR (1)\nS → A a |b A c |B c | b B a\nA → d\nB → d
• Count number of pairs (A <= N, B <= N) such that gcd (A , B) is B in C++
• Construct a Finite Automata for the regular expression ((a+b)(a+b))*.
• A += B Assignment Riddle in Python
• Find a palindromic string B such that given String A is a subsequence of B in C++
• Check if a string follows a^n b^n pattern or not in Python
• Construct a PDA that accepts (a,b)* language but not contain bbbb?
• Count pairs (a, b) whose sum of squares is N (a^2 + b^2 = N) in C++
• Count pairs (a, b) whose sum of cubes is N (a^3 + b^3 = N) in C++
• Print values of ‘a’ in equation (a+b) <= n and a+b is divisible by x
• a.sort, sorted(a), np_argsort(a) and np.lexsort(b, a) in Python
• Check if a + b = c is valid after removing all zeroes from a, b and c in C++
• Find all pairs (a, b) in an array such that a % b = k in C++