Python 3.10: Cool New Features for You to Try

Python 3.10: Cool New Features for You to Try

by Geir Arne Hjelle 55m intermediate python

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Cool New Features in Python 3.10 (58m)

Python 3.10 is out! Volunteers have been working on the new version since May 2020 to bring you a better, faster, and more secure Python. As of October 4, 2021, the first official version is available.

Each new version of Python brings a host of changes. You can read about all of them in the documentation. Here, you’ll get to learn about the coolest new features.

In this tutorial, you’ll learn about:

  • Debugging with more helpful and precise error messages
  • Using structural pattern matching to work with data structures
  • Adding more readable and more specific type hints
  • Checking the length of sequences when using zip()
  • Calculating multivariable statistics

To try out the new features yourself, you need to run Python 3.10. You can get it from the Python homepage. Alternatively, you can use Docker with the latest Python image.

Better Error Messages

Python is often lauded for being a user-friendly programming language. While this is true, there are certain parts of Python that could be friendlier. Python 3.10 comes with a host of more precise and constructive error messages. In this section, you’ll see some of the newest improvements. The full list is available in the documentation.

Think back to writing your first Hello World program in Python:

Python 
# hello.py

print("Hello, World!)

Maybe you created a file, added the famous call to print(), and saved it as hello.py. You then ran the program, eager to call yourself a proper Pythonista. However, something went wrong:

Shell 
$ python hello.py
  File "/home/rp/hello.py", line 3
    print("Hello, World!)
                        ^
SyntaxError: EOL while scanning string literal

There was a SyntaxError in the code. EOL, what does that even mean? You went back to your code, and after a bit of staring and searching, you realized that there was a missing quotation mark at the end of your string.

One of the more impactful improvements in Python 3.10 is better and more precise error messages for many common issues. If you run your buggy Hello World in Python 3.10, you’ll get a bit more help than in earlier versions of Python:

Shell 
$ python hello.py
  File "/home/rp/hello.py", line 3
    print("Hello, World!)
          ^
SyntaxError: unterminated string literal (detected at line 3)

The error message is still a bit technical, but gone is the mysterious EOL. Instead, the message tells you that you need to terminate your string! There are similar improvements to many different error messages, as you’ll see below.

A SyntaxError is an error raised when your code is parsed, before it even starts to execute. Syntax errors can be tricky to debug because the interpreter provides imprecise or sometimes even misleading error messages. The following code is missing a curly brace to terminate the dictionary:

Python 
 1# unterminated_dict.py
 2
 3months = {
 4    10: "October",
 5    11: "November",
 6    12: "December"
 7
 8print(f"{months[10]} is the tenth month")

The missing closing curly brace that should have been on line 7 is an error. If you run this code with Python 3.9 or earlier, you’ll see the following error message:

Python Traceback 
  File "/home/rp/unterminated_dict.py", line 8
    print(f"{months[10]} is the tenth month")
    ^
SyntaxError: invalid syntax

The error message highlights line 8, but there are no syntactical problems in line 8! If you’ve experienced your share of syntax errors in Python, you might already know that the trick is to look at the lines before the one Python complains about. In this case, you’re looking for the missing closing brace on line 7.

In Python 3.10, the same code shows a much more helpful and precise error message:

Python Traceback 
  File "/home/rp/unterminated_dict.py", line 3
    months = {
             ^
SyntaxError: '{' was never closed

This points you straight to the offending dictionary and allows you to fix the issue in no time.

There are a few other ways to mess up dictionary syntax. A typical one is forgetting a comma after one of the items:

Python 
 1# missing_comma.py
 2
 3months = {
 4    10: "October"
 5    11: "November",
 6    12: "December",
 7}

In this code, a comma is missing at the end of line 4. Python 3.10 gives you a clear suggestion on how to fix your code:

Python Traceback 
  File "/home/real_python/missing_comma.py", line 4
    10: "October"
        ^^^^^^^^^
SyntaxError: invalid syntax. Perhaps you forgot a comma?

You can add the missing comma and have your code back up and running in no time.

Another common mistake is using the assignment operator (=) instead of the equality comparison operator (==) when you’re comparing values. Previously, this would just cause another invalid syntax message. In the newest version of Python, you get some more advice:

Python 
>>> if month = "October":
  File "<stdin>", line 1
    if month = "October":
       ^^^^^^^^^^^^^^^^^
SyntaxError: invalid syntax. Maybe you meant '==' or ':=' instead of '='?

The parser suggests that you maybe meant to use a comparison operator or an assignment expression operator instead.

Take note of another nifty improvement in Python 3.10 error messages. The last two examples show how carets (^^^) highlight the whole offending expression. Previously, a single caret symbol (^) indicated just an approximate location.

The final error message improvement that you’ll play with for now is that attribute and name errors can now offer suggestions if you misspell an attribute or a name:

Python 
>>> import math
>>> math.py