Recently, there have been a few proposals to change Python's syntax to make it easier to avoid break and continue statements.

The reasoning seems to be that many people are taught never to use break and continue, or to only have a single break in any loop. Some of these people are in fact forced to follow these rules for class assignments.

These rules are ludicrous. The stdlib has hundreds of break and continue statements. There are dozens of them in the official tutorial, the library reference docs, Guido's blogs, etc. The reasons for avoiding break and continue in other languages don't apply to Python, and many of the ways people use to avoid them don't even exist in Python. Using break and continue appropriately is clearly Pythonic.

The python-ideas community tracked these rules back to some misguided attempts to apply the rules from MISRA-C to Python.

It should be obvious that C and Python are very different languages, with different appropriate idioms, so applying MISRA-C to Python is insanely stupid. But, in case anyone doesn't get it, I've gone through the requirements and recommendations in MISRA-C 1998. By my count, more than half of them don't even mean anything in Python (e.g., rules about switch statements or #define macros), and more than half of the rest are bad rules that would encourage non-Pythonic code.

I've paraphrased them, both to avoid violating the copyright on the document, and to express them in Python terms:
  • 8. req: No unicode, only bytes, especially in literals. (In other words, '\u5050' is bad; b'\xe5\x81\x90' is good.)
  • 12. rcm: Don't use the same identifier in multiple namespaces. (For example, io.open and gzip.open should not have the same name, nor should two different classes ever have members or methods with the same name.)
  • 13. rcm: Never use int when you can use long. (Only applies to Python 2.x.)
  • 18. rcm: Suffix numeric literals. (Only applies to Python 2.x.)
  • 20. req: Declare all variables and functions at the top of a module or function.
  • 31. req: Use curly braces in all initializers. (Sorry, no lists allowed, just dicts and sets.)
  • 33. req: Never use a user-defined function call on the right side of logical and/or.
  • 34. req: Never use anything but a primary expression on either side of logical and/or.
  • 37. req.: Never use bitwise operators on signed types (like int).
  • 47. rcm: Never rely on operator precedence rules.
  • 48. rcm: Use explicit conversions when performing arithmetic between multiple types.
  • 49. rcm: Always test non-bool values against False instead of relying on truthiness.
  • 53. req: All statements should have a side-effect.
  • 57. req: No continue.
  • 58. req: No break.
  • 59. req: No one-liner if and loop bodies.
  • 60. rcm: No if/elif without else.
  • 67. rcm: Don't rebind the iterator in a for loop.
  • 68. req: All functions must be at file scope.
  • 69. req: Never use *args in functions.
  • 70. req: No recursion.
  • 82. rcm: Functions should have a single point of exit.
  • 83. req: No falling off the end of a function to return None.
  • 86. rcm: Always test function returns for errors.
  • 104. req: No passing functions around.
  • 118. req: Never allocate memory on the heap.
  • 119. req: Never rely on the errno in an OSError (or handle FileNotFoundError separately, etc.).
  • 121. req: Don't use locale functions.
  • 123. req: Don't use signals.
  • 124. req: Don't use stdin, stdout, etc., including print.
  • 126. req: Don't use sys.exit, os.environ, os.system, or subprocess.*.
  • 127. req: Never use Unix-style timestamps (e.g., time.time()).


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It's been more than a decade since Typical Programmer Greg Jorgensen taught the word about Abject-Oriented Programming.

Much of what he said still applies, but other things have changed. Languages in the Abject-Oriented space have been borrowing ideas from another paradigm entirely—and then everyone realized that languages like Python, Ruby, and JavaScript had been doing it for years and just hadn't noticed (because these languages do not require you to declare what you're doing, or even to know what you're doing). Meanwhile, new hybrid languages borrow freely from both paradigms.

This other paradigm—which is actually older, but was largely constrained to university basements until recent years—is called Functional Addiction.
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I haven't posted anything new in a couple years (partly because I attempted to move to a different blogging platform where I could write everything in markdown instead of HTML but got frustrated—which I may attempt again), but I've had a few private comments and emails on some of the old posts, so I decided to do some followups.

A couple years ago, I wrote a blog post on greenlets, threads, and processes.
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Looking before you leap

Python is a duck-typed language, and one where you usually trust EAFP ("Easier to Ask Forgiveness than Permission") over LBYL ("Look Before You Leap"). In Java or C#, you need "interfaces" all over the place; you can't pass something to a function unless it's an instance of a type that implements that interface; in Python, as long as your object has the methods and other attributes that the function needs, no matter what type it is, everything is good.
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Background

Currently, CPython’s internal bytecode format stores instructions with no args as 1 byte, instructions with small args as 3 bytes, and instructions with large args as 6 bytes (actually, a 3-byte EXTENDED_ARG followed by a 3-byte real instruction). While bytecode is implementation-specific, many other implementations (PyPy, MicroPython, …) use CPython’s bytecode format, or variations on it.

Python exposes as much of this as possible to user code.
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If you want to skip all the tl;dr and cut to the chase, jump to Concrete Proposal.

Why can’t we write list.len()? Dunder methods C++ Python Locals What raises on failure? Method objects What about set and delete? Data members Namespaces Bytecode details Lookup overrides Introspection C API Concrete proposal CPython Analysis

Why can’t we write list.len()?

Python is an OO language. To reverse a list, you call lst.reverse(); to search a list for an element, you call lst.index().
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Many people, when they first discover the heapq module, have two questions:

Why does it define a bunch of functions instead of a container type? Why don't those functions take a key or reverse parameter, like all the other sorting-related stuff in Python? Why not a type?

At the abstract level, it's often easier to think of heaps as an algorithm rather than a data structure.
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Currently, in CPython, if you want to process bytecode, either in C or in Python, it’s pretty complicated.

The built-in peephole optimizer has to do extra work fixing up jump targets and the line-number table, and just punts on many cases because they’re too hard to deal with. PEP 511 proposes a mechanism for registering third-party (or possibly stdlib) optimizers, and they’ll all have to do the same kind of work.
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One common "advanced question" on places like StackOverflow and python-list is "how do I dynamically create a function/method/class/whatever"? The standard answer is: first, some caveats about why you probably don't want to do that, and then an explanation of the various ways to do it when you really do need to.

But really, creating functions, methods, classes, etc. in Python is always already dynamic.

Some cases of "I need a dynamic function" are just "Yeah? And you've already got one".
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A few years ago, Cesare di Mauro created a project called WPython, a fork of CPython 2.6.4 that “brings many optimizations and refactorings”. The starting point of the project was replacing the bytecode with “wordcode”. However, there were a number of other changes on top of it.

I believe it’s possible that replacing the bytecode with wordcode would be useful on its own.
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Many languages have a for-each loop. In some, like Python, it’s the only kind of for loop:

for i in range(10): print(i) In most languages, the loop variable is only in scope within the code controlled by the for loop,[1] except in languages that don’t have granular scopes at all, like Python.[2]

So, is that i a variable that gets updated each time through the loop or is it a new constant that gets defined each time through the loop?

Almost every language treats it as a reused variable.
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