Hi everyone why does it give error?

Question

https://sololearn.com/compiler-playground/c436DxiiU78C/?ref=app
Note when I tried elif it worked well.

Answer 1

import sys
print(sys.version)

# What do you observe?
# What does it tell you about your present issue?

Answer 2

match...case it is used in the newer version of python 3.10.

Answer 3

Yusof ,

Sololearn apparently upgraded from 3.9.16 to 3.9.18 five days ago, but it's still too low to use the match compound statement.

If you're on Android, as I am, you can download Pydroid 3 from the Google Play Store.

It's a Python 3 IDE for Android. It's free with ads, or trial subscription becomes subscription (don't start that), or pay once for life (better deal). The ads don't play in airplane mode.

Pydroid 3 is currently running Python 3.11.4. I've experimented with match there.

Answer 4

"Match" is similar (not equal) not the "switch" in other language.
https://docs.python.org/3/tutorial/controlflow.html#tut-match

In the given code, "n" is a string, while "n.endswith(...)" is a boolean. The case values would need to be of the same type as the match value.

Answer 5

Yusof ,

Here's a refactoring that does the same job, but I won't be satisfied until I also understand why,

match True:

doesn't fix the TypeError in your first version.

https://sololearn.com/compiler-playground/cffGkCrIwZvU/?ref=app

Answer 6

Wong Hei Ming ,

Yeah, but I'm talking about the substitution to his original code that Solo mentioned and I had already tried without success.

Original code:

n=input("enter file : ").lower()
match n:
case n.endswith(".gif"):
print("image/gif")
case n.endswith(".jpg"):
print("jpeg/image")
case n.endswith(".jpeg"):
print("jpeg/image")
case n.endswith(".ping"):
print("jpeg/image")
case n.endwith(".pdf"):
print("pdf/text")
case n.endswith(".txt"):
print("txt/text")
case n.endswith(".zip"):
print("zip/text")
case _:
print("applicaton/octet-stream")

That gets a TypeError, which one would think is because it tries to match str to bool.

So you change it from,
match n:
to,
match True:
in order to match bool to bool. Like so.

n=input("enter file : ").lower()
match True:
case n.endswith(".gif"):
print("image/gif")
case n.endswith(".jpg"):
print("jpeg/image")

[etc.]

but it still gets TypeError.

What causes that TypeError?

Answer 7

I tried it on online visual studio code it gives me type errorSolo

Answer 8

Yusof, try match True: ...😎

Answer 9

Solo ,

Did you get match True: to work? I thought of it too, but it still produced the same error for me.

TypeError: called match pattern must be a type

Answer 10

Rain, no, this is just my guess, (I had neither the opportunity nor the time to check it).
Based on logic "match n case n.endswith(".gif"):" – this is similar to the "if 'file.gif' == True:", which in principle is not true to compare, whereas "if True == True:" could fix the situation, since the method .endswith() returns a Boolean value.

Personally, I would use a dictionary here instead of a match...case, it's much simpler and more ergonomic in my opinion.

Answer 11

Solo ,

Yeah that's what I was trying too: since all the cases evaluate to bool, why not make the match bool? But the problem is apparently deeper and weirder.

Answer 12

Just tried with IDLE.
In the below code the first case runs, not the second.

n=input("enter file : ").lower()
match n:
case ".gif":
print("image/gif")
case n.endswith(".jpg"):
print("jpeg/image")

# It runs if the input of n is ".gif", but not "somevalue.jpg"

Answer 13

Rain
It should be match n: not match True:

n = True
match n:
case True:
print(True)
case False:
print(False)
case _:
print("Something else")

It prints True

Answer 14

You could

Answer 15

Add more like false and true code

Answer 16

Rain
I take a little time to look for the documentation and found this.
https://docs.python.org/3/reference/compound_stmts.html#match

Under 8.6.4.10, it says:
If name_or_attr is not an instance of the builtin type , raise TypeError.

My guess (probably wrong), match True: where the "True" in the statement is not an instance.