How Python’s + Operator Concatenates Strings (and Why Numbers Fail)

Python “+” operator on strings

Using + between two string objects concatenates them into a single string.

str1 = "hello"
str2 = "world"
print(str1 + str2)

Output: hello world Adding a string and an integer raises TypeError because Python does not support addition between a string and a numeric type.

str3 = "welcome"
num = 12
# print(str3 + num)  # raises TypeError

Resulting traceback (escaped tag):

Traceback (most recent call last):
  File "C:/Users/xuexi/Desktop/python/xuexi007.py", line 8, in <module>
    print(str3 + num)
TypeError: can only concatenate str (not "int") to str
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