What's the difference between raise, try, and assert?

Question

I have been learning Python for a while and the raise function and assert are (what I realised is that both of them crash the app, unlike try - except) really similar and I can't see a situation where you would use raise or assert over try.

So, what is the difference between raise, try, and assert?

Answer 1

Assert:

Used when you want to "stop" the script based on a certain condition and return something to help debug faster:

list_ = ["a","b","x"]
assert "x" in list_, "x is not in the list"
print("passed") 
#>> prints passed

list_ = ["a","b","c"]
assert "x" in list_, "x is not in the list"
print("passed")
#>> 
Traceback (most recent call last):
  File "python", line 2, in <module>
AssertionError: x is not in the list

---

Raise:

Two reasons where this is useful:

1/ To be used with try and except blocks. Raise an error of your choosing, could be custom like below and doesn't stop the script if you pass or continue the script; or can be predefined errors raise ValueError()

class Custom_error(BaseException):
    pass

try:
    print("hello")
    raise Custom_error
    print("world")
except Custom_error:
    print("found it not stopping now")

print("im outside")

>> hello
>> found it not stopping now
>> im outside

Noticed it didn't stop? We can stop it using just exit(1) in the except block.

2/ Raise can also be used to re-raise the current error to pass it up the stack to see if something else can handle it.

except SomeError, e:
     if not can_handle(e):
          raise
     someone_take_care_of_it(e)

---

Try/Except blocks:

Does exactly what you think, tries something if an error comes up you catch it and deal with it however you like. No example since there's one above.