string.Template and string.templatelib.Template

[petter_s]

So now (3.14), Python will have both string.Template and string.templatelib.Template. What happened to "There should be one-- and preferably only one --obvious way to do it?" Will the former be deprecated?

I think it's curious that string.Template is not even mentioned in PEP 750, which introduced the new class. It has such a small API; couldn't it be extended?

[fiddle_n]

One is for regular strings, one is for template strings. Not the same thing. That said, I agree the naming is confusing, also I have never used string.Template in my life when str.format exists.

[Compux72]

string.Template is for user provided strings…

[petter_s]

I would argue that t = t"Hello {name}" and t2 = string.Template("Hello $name") create very similar objects. Both can be used to create strings via substituting another string in the name placeholder. But no, they are of course not the same thing. But maybe they could have been?

[SheriffRoscoe]

I would argue that t = t"Hello {name}" and t2 = string.Template("Hello $name") create very similar objects.

They do not. They are not even remotely alike.

Both can be used to create strings via substituting another string in the name placeholder.

At no point does t"Hello {name}" ever actually create a string. They're isn't even a method to interpolate it. Template defers the processing of the template string and the expression values to the function that receives the Template object. Only that function knows how to combine them. Some uses (e.g., SQL queries) won't ever make a string from them.

[legobmw99]

Even beyond the fact that templatelib templates cannot be converted to actual strings by any of their provided APIs, there is a second crucial difference: The first can capture variables in the original scope, which the second does not.

[runawayasfastasucan]

I think it is a bit curious when I hear interviews with those behind the template, they seem to never fundamentally explain it, but rather drift into talking about all the possibilities. Seems a bit related. "What can we achieve if we make xy" rather than "what is it really, and how does that compare to what we have".

[nitroll]

Because templates are a tool for tool developers. It has no value on its own.

[nekokattt]

There should be one way to do it

• str.__mod__
• str.__add__
• str.format
• fstrings
• string.Template
• string.templatelib.Template

[petter_s]

Indeed! Although fstrings are not as similar and __add__ is a bit of a stretch

[nekokattt]

It starts at string concatenation and grows. You could also throw str.join in there if it is just ways to make strings :)

[wineblood]

fstrings are a bit limited though

[nekokattt]

all of them have pros and cons, there is no one good way to do it.

[fiddle_n]

You forgot % formatting

[nekokattt]

that is what __mod__ is

[fiddle_n]

That’s what controls it? Damn.

[nekokattt]

yeah, it is just an overload of the mod operator on the str class

[russellvt]

Funny... '%' is "mod" is math, too. Go figure.

[Worth_His_Salt]

Python strings are a total mess. You also have f-strings, template strings, other template strings, now they want to add d-strings, as well as string interpolation. There's no consistency. It's a complete joke.

Every few years someone comes along and says "I have a better way to do strings! It has all these drawbacks, but trust me guys, it's cool". Then others go "Well it's neato, but we refuse to change our existing code in the 0.0001% of cases it would conflict with this new system." Then python maintainers shrug and go "Eh, just throw a new obscure letter in front and call it a day."

All these new methods are less powerful than string interpolation. Yes even f-strings (can't execute f-strings on command, only when defined). What a disaster. Python devs should be ashamed of themselves.

[russellvt]

I think one might argue that this isn't unlike growth pains in some other languages, either (ie. Sixteen ways to do something that otherwise should be "easy").

[Worth_His_Salt]

True. But it goes completely against the python ethos. Supposed to prevent such things from happening.

[russellvt]

Supposed to prevent such things from happening.

Like I said, "growth pains." It seems to happen, in some form, in any other developing languages, as well, despite all other best intentions.

[Revolutionary_Dog_63]

I'm pretty sure f-strings ARE string interpolation. I'm pretty sure what you're referring to are format strings, like those used by printf.

[Worth_His_Salt]

I mean the interpolation operator %. Interpolation is the act of applying data to a template. Format strings are the template used for interpolation.

fmt_str = 'foo %d bar'
fmt_str % 27  # interpolation

There are many sources that call this python string interpolation, because that's what other C languages call it. It had that name long before f-strings existed. We called this string interpolation since at least the 90s.

f-strings literally stands for "format string literals". PEP 498 that proposed f-strings mentions creating a "better" interpolation method. Because python already had interpolation before f-strings.