This post is courtesy of Shivansh Singh, Partner Solutions Architect – AWS

We are excited to announce that you can now develop your AWS Lambda functions using the Python 3.7 runtime. Start using this new version today by specifying a runtime parameter value of “python3.7″ when creating or updating functions. AWS continues to support creating new Lambda functions on Python 3.6 and Python 2.7.

Here’s a quick primer on some of the major new features in Python 3.7:

• Data classes
• Customization of access to module attributes
• Typing enhancements
• Time functions with nanosecond resolution

Data classes

In object-oriented programming, if you have to create a class, it looks like the following in Python 3.6:

class Employee:
    def __init__(self, name: str, dept: int) -> None:
        self.name = name
        self.dept = dept
        
    def is_fulltime(self) -> bool:
        """Return True if employee is a Full-time employee, else False"""
        return self.dept > 25

The __init__

With Python 3.7, you have dataclasses, which make class declarations easier and more readable. You can use the @dataclass decorator on the class declaration and self-assignment is taken care of automatically. It generates __init__, __repr__, __eq__, __hash__, and other special methods. In Python 3.7, the Employee class defined earlier looks like the following:

@dataclass
Class Employee:
    name: str
    dept: int
    
    def is_fulltime(self) -> bool:
        """Return True if employee is a Full-time employee, else False"""
        return self.dept > 25

Customization of access to module attributes

Attributes are widely used in Python. Most commonly, they used in classes. However, attributes can be put on functions and modules as well. Attributes are retrieved using the dot notation: something.attribute. You can also get attributes that are named at runtime using the getattr() function.

For classes, something.attr first looks for attr defined on something. If it’s not found, then the special method something.__getattr__(“attr”) is called. The .getattr__() function can be used to customize access to attributes on objects. This customization is not easily available for module attributes, until Python 3.7. But PEP 562 provides __getattr__() on modules, along with a corresponding __dir__() function.

Typing enhancements

Type annotations are commonly used for code hints. However, there were two common issues with using type hints extensively in the code:

• Annotations could only use names that were already available in the current scope. In other words, they didn’t support forward references.
• Annotating source code had adverse effects on the startup time of Python programs.

Both of these issues are fixed in Python 3.7, by postponing the evaluation of annotations. Instead of compiling code that executes expressions in annotations at their definition time, the compiler stores the annotation in a string form equivalent to the AST of the expression in question.

For example, the following code fails, as spouse cannot be defined as type Employee, given that Employee is not defined yet.

class Employee:
    def __init__(self, name: str, spouse: Employee) --> None
        pass

In Python 3.7, the evaluation of annotation is postponed. It gets stored as a string and optionally evaluated as needed. You do need to import __future__, which breaks the backward compatibility of the code with previous versions of Python.

from __future__ import annotations

class Employee:
    def __init__(self, name: str, spouse: Employee) --> None
        pass

Time functions with nanosecond resolution

The time module gets some new functions in Python 3.7. The clock resolution can exceed the limited precision of a floating point number returned by the time.time() function and its variants. The following new functions are being added:

• clock_gettime_ns()
• clock_settime_ns()
• monotonic_ns()
• perf_counter_ns()
• process_time_ns()
• time_ns()

These functions are similar to already existing functions without the _ns suffix. The difference is that the above functions return a number of nanoseconds as an int instead of a number of seconds as a float.

Hope you enjoy… go build with Python 3.7!