Think about the result of this snippet:

def concat(a, b):
    return a + "_" + b
left = "hello",
right = "world"
print(concat(left, right))

Should be “hello_world”, right?

But the actual result is an error:

Traceback (most recent call last):
  File "test.py", line 7, in <module>
    print(concat(left, right))
  File "test.py", line 2, in concat
    return a + "_" + b
TypeError: can only concatenate tuple (not "str") to tuple

and the error seems hard to understand.

As a matter of fact, the reason for this error is we have just put a comma after “hello” so the value of variable “left” is a tuple (“hello”,) instead of a string “hello”

Even for this shortcode sample, it is hard to find the reason, not mention in the real program to find out the root. For the first time in recent 3 years, I began to miss the strong-type programming language like C…

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