How to print an exception in Python 3?

These are the changes since python 2:

    try:
        1 / 0
    except Exception as e: # (as opposed to except Exception, e:)
                           # ^ that will just look for two classes, Exception and e
        # for the repr
        print(repr(e))
        # for just the message, or str(e), since print calls str under the hood
        print(e)
        # the arguments that the exception has been called with. 
        # the first one is usually the message. (OSError is different, though)
        print(e.args)

You can look into the standard library module traceback for fancier stuff.

I'm guessing that you need to assign the Exception to a variable. As shown in the Python 3 tutorial:

def fails():
    x = 1 / 0

try:
    fails()
except Exception as ex:
    print(ex)

To give a brief explanation, as is a pseudo-assignment keyword used in certain compound statements to assign or alias the preceding statement to a variable.

In this case, as assigns the caught exception to a variable allowing for information about the exception to stored and used later, instead of needing to be dealt with immediately.

(This is discussed in detail in the Python 3 Language Reference: The try Statement.)

---

There are other compound statements that use as. The first is the with statement:

@contextmanager
def opening(filename):
    f = open(filename)
    try:
        yield f
    finally:
        f.close()

with opening(filename) as f:
    # ...read data from f...

Here, with statements are used to wrap the execution of a block with methods defined by context managers. This functions like an extended try...except...finally statement in a neat generator package, and the as statement assigns the generator-produced result from the context manager to a variable for extended use.

(This is discussed in detail in the Python 3 Language Reference: The with Statement.)

---

As of Python 3.10, match statements also use as:

from random import randint

match randint(0, 2):
    case 0|1 as low:
        print(f"{low} is a low number")
    case _:
        print("not a low number")

match statements take an expression (in this case, randint(0, 2)) and compare its value to each case branch one at a time until one of them succeeds, at which point it executes that branch's block. In a case branch, as can be used to assign the value of the branch to a variable if that branch succeeds. If it doesn't succeed, it is not bound.

(The match statement is covered by the tutorial and discussed in detail in the Python 3 Language Reference: match Statements.)

---

Finally, as can be used when importing modules, to alias a module to a different (usually shorter) name:

import foo.bar.baz as fbb

This is discussed in detail in the Python 3 Language Reference: The import Statement.