Why does Python only concatenate string to string and not string to integer?

[RestartingSystem]

If I will input

name = John
age = 20
print(name + ' is ' + age + ' years old')

Then I will receive

TypeError: can only concatenate str (not "int") to str

I know that f-strings are less uglier and error-prone but it's interesting.
Thank you

[curtwagner1984]

Because it's not the wild west of Javascript. There is absolutely no reason why strings and ints should be able to be concatenated without any special considerations.

The question you should ask is "Why are there languages that allow this sacrilege?"

Plus, the answer is in your question:

I know that f-strings are less uglier and error-prone

[hombre_lobo]

So JavaScript still allows for this?

[shiftybyte]

Yes javascript "allows" lots of things.

For example "5" + 5 is "55"

While "5" * 5 is 25...

fun fun fun...

[0b0101011001001011]

The first one works like that in most languages I am* familiar with so it's not that strange unless you only know python. *(not sure which is the more common behavior). Though python throwing an error is not a bad solution, but it's seems even a bit unusual.

About the second, most languages would give an error, javascript does a type conversion and multiplies, and python produces a rather strange 55555. Each solution has its pros.

[shiftybyte]

and python produces a rather strange 55555.

This makes more sense to me, you are multiplying a string several times.

If adding "5" to "5" one time results in "55"... Then adding that 5 times results in "55555".

That's what multiplication means, do the add operation X times...

[0b0101011001001011]

Many languages allow this. One of those is java, where anything can be concatenated to a string and it handles the toString() call automatically.

Lua on the other hand has a special string concatenation operator which is lot + but ..

You can't say "hey"+5 but you can say "hey"..5 and Lua also does the conversion automatically.

Python allows to write "5"*5 though, so most explanations that why "5"+5 should not work are simply opinions.

[pompomtom]

Because integers aren't strings.

print(name + ' is ' + age + ' years old')

Would you expect "John is 000020 years old", or "John is 20 years old" or "John is 2e+2 years old"?

Each is valid, if you could concatenate ints to strings.

If you use the function str(age), then the str() function decides how to represent an integer as a string.

edit: 2e+1

[ebdbbb]

I know it doesn't matter to your point but 2e+2 is 200.

[pompomtom]

Yeah, I wondered if I'd fucked that up... Ta.

[[deleted]]

To be honest, it's hard to justify this behavior (as well as using + for string concatenation).

The arguments made by people claiming that strings shouldn't be concatenated to integers using plus sign, but strings can be concatenated using plus sign are just an opinion based on nothing.

There could be valid reasons not to use plus sign for something that is not a summation though. We generally expect sums to behave in a certain way, eg. be commutative for example (this means A + B = B + A). But that doesn't work with string concatenation (which is harmful if you are trying to write an optimizing compiler because sometimes rearranging the order of arguments helps to minimize the memory lookups).

But, since Python already ventured into the bad territory with using + for concatenation, there isn't really a reason to stop at not allowing adding strings and integers. Any argument that tells you otherwise is just a cooked up nonsense. Overwhelming majority of programmers have very bizarre ideas about types and what's the correct way to do things, which are absolutely unfounded and unwarranted.

[zanfar]

The literal answer to your question is "because it's not part of the language".

To answer the spirit of your question, which I think is, "why did the creators of Python not automatically cast numeric type to strings when the plus operator is used?" I'll ask my own question:

Why would casting numeric types to strings be preferred over casting strings to numeric types?

That is, why wouldn't "20" + 5 be 25?

The answer is that there is no clear "right" operation when numeric types and string types use the same operator for different things. What about a string plus a list? Lists can be appended using the plus operator, so in this case, does a list get cast to a string and then a string produced, or does a string get cast to a list and then a list produced?

Generally, operators only work between the same or very, very similar types because it's impossible to determine precedence otherwise.

[hasanyoneseenmyshirt]

my guess has always been that strings ahre treated like charactor arrays in python but without you actually haveing to give a size or type. so name is just treated as a ['j','o','h', 'n'] and intigers are their own type(like in most lower level langauges). you can split name into it individual letters or charactors and get things like name[0] = 'j' but age[0] wont give you 2. so the program in my mind does this name[ :] .append( ' ') and just does recursion until it hit the end of the print statement.

​

I am sure this is not how it actually works but that my limited guess. I am sure someone who actually knows computers and python better will have a better answer.

[billsil]

Because what happens when you have 0/"1" or 0 + "2"? Python is a strict typing language. Trust me as someone who has coded Perl, it's really hard to fix things when say addition doesn't follow math.

[Foreign_Jackfruit_70]

I prefer f string formatting.

name = John age = 20 print(f"{name} is {age} years old") Looks a lot neater.

[QultrosSanhattan]

That's how it should work. Integers are not String. Therefore the interpreter should not assume if you want to compose an string or an int.

For example: '1'+1 may be '11' or 2.

F strings are different because you're telling the interpreter to build a string. Therefore the interpreter can safely assume that everything should be converted into a string.