Raymond Hettinger @raymondh Twitter profile

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Raymond Hettinger

2 months

#Python tip: If you were to devote a little effort into mastering just one itertool, it should be islice(). Its motivation was to be an analogue of sequence slicing but with next-in-a-loop as the foundation rather than __getitem__() and __len__().

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Raymond Hettinger

@raymondh

5 years

#Python 's f-strings are amazingly fast! f'{s} {t}' # 78.2 ns s + ' ' + t # 104 ns ' '.join((s, t)) # 135 ns '%s %s' % (s, t) # 188 ns '{} {}'.format(s, t) # 283 ns Template('$s $t').substitute(s=s, t=t) # 898 ns

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Raymond Hettinger

@raymondh

7 years

#python news: 😀 @gvanrossum just pronounced that dicts are now guaranteed to retain insertion order. This is the end of a long journey.

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@raymondh

6 years

#Python tip: If your data is in a dictionary, perhaps from a JSON file, then str.format_map() is your new best friend. Pretty way: print('{name} works at {status} {company}'.format_map(info)) Less pretty: print(f'{info["name"]} works at {info["status"]} {info["company"]}')

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@raymondh

5 years

Woohoo! #Python 3.8 was just released. And on the same day that PyPI hit 200,000 packages :-) This one really is the best Python ever. Download it now.

Python Release Python 3.8.0

The official home of the Python Programming Language

www.python.org

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@raymondh

5 years

#Python 3.8 news: F-strings now have a "=" specifier that prints an expression and its result. Very handy for diagnostic prints: >>> print(f'{alpha=} {beta=} {betavariate(alpha, beta)=:.3f}') alpha=3 beta=7 betavariate(alpha, beta)=0.256

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@raymondh

6 years

#Python 2.7 reaches end-of-life at the end of 2019. Afterwards, the interpreter will not get updates -- no bugfixes, no security fixes, nothing. In the interim, the Python ecosystem is abandoning 2.7 support. Don't wait to switch to Python 3.

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@raymondh

4 years

1/ #Python tip: Join sequences with itertools.chain() instead of with addition: list(chain(a, b, c, d, e)) # O(n) a + b + c + d + e # O(n²)

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@raymondh

5 years

#Python security: eval() is powerful, don't feed it untrusted inputs. "import" is powerful, don't import untrusted modules. "pickle" is powerful, don't unpickle untrusted data. Programmable computers are powerful, don't run untrusted programs.

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Raymond Hettinger

@raymondh

3 years

Computer experts on TV and Movies seem to magically know things. You don't see them reading books, attending conferences, contributing to open source, debugging code, taking classes, working collaboratively, refactoring, or using StackOverflow.

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Raymond Hettinger

@raymondh

4 years

#Python tip: The int() function is smarter than it looks: >>> int('42') 42 >>> int('४२') 42 >>> int('٤٢') 42

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Raymond Hettinger

@raymondh

6 years

Writing production #python code: * Simplest thing that works * Consider type signatures * Add repr, copy, and pickle support. * Watch out for circular references * Think hard about concurrency * Handle exotic and unanticipated use cases * Learn from the experience * Repeat

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@raymondh

5 years

#Python tip: Regular expressions can be challenging to learn, to read, and to debug. My friend @r1chardj0n3s wrote a parse module that is much easier to work with. It's suitable for everyday parsing tasks when you don't need the full power of regexes:

parse

parse() is the opposite of format()

pypi.org

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@raymondh

6 years

#python 3.8 news: Python containers are 8 bytes smaller on 64-bit builds. [] 64 ⟶ 56 () 48 ⟶ 40 {} 240 ⟶ 232 set() 224 ⟶ 216 Many thanks to Naoki Inada for looking carefully at the GC code.

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@raymondh

1 year

If all goes well, tomorrow #Python 3.12 will be released as final :-)

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@raymondh

4 years

My 8 year old demanded another algorithm, so tonight we’re doing Langston’s Ant. #Python #Homeschooling

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Raymond Hettinger

@raymondh

4 years

Over time, the #python world has shown increasing preference for double quotes: "hello" versus 'hello'. Perhaps, this is due to the persistent influence of JSON, PyCharm, Black, and plain English. In contrast, the interpreter itself prefers single quotes: >>> "hello" 'hello'

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@raymondh

4 years

#Python factlet: All objects are born true. They have to learn to be false either with a __bool__() method that returns False or a __len__() method that returns 0.

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@raymondh

6 years

Today's super-easy #python student question. Q. What are the best practices for modifying a list while looping over it? A. Don't. Seriously, just make a new list and avoid hard-to-read code with hard-to-find bugs.

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@raymondh

5 years

#python threading tip: To loop over a dictionary in isolation from other threads, prefer: for k, v in d.copy().items(): ... instead of: for k, v in list(d.items()): ... The copy() is atomic and avoids: RuntimeError: dictionary changed size during iteration

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@raymondh

4 years

#Python tip: Slice's are objects. You can store them in variables or containers just as you would with a regular integer index. >>> s = slice(6, 12) >>> title = "Monty python's flying circus" >>> title[s] 'python'

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@raymondh

6 years

#python tip: It is easy to capture the output of functions that print to the terminal: with open('help.txt', 'w') as f: with contextlib.redirect_stdout(f): help(pow)

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@raymondh

6 years

#python tip: f-strings are surprisingly fast: $ python3.7 -m timeit -s 'x=6' 'str(x)' 2000000 loops, best of 5: 187 nsec per loop $ python3.7 -m timeit -s 'x=6' 'f"{x}"' 5000000 loops, best of 5: 75.9 nsec per loop

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@raymondh

3 years

#Python tip: Debuggers are wonderful, but sometimes just adding "print(locals())" is the easiest way to go ;-)

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Raymond Hettinger

@raymondh

4 years

#Python optimization news: Inline caching has been a huge success. In 3.9, access to builtins and globals had sped-up considerably. In 3.10, regular attribute access and access to __slots__ are also faster. Most everyday Python programs will benefit. This is a huge win.

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Raymond Hettinger

@raymondh

6 years

I started contributing to #Python when I was 36 years old. Today is my birthday and I’m now 0x36. #gottalovehex

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Raymond Hettinger

@raymondh

5 years

#python tip: list.remove() deletes the first match and then shifts all subsequent data one position to the left. In a loop, that gives quadratic behavior: There's a better way to remove all matches: data[:] = [elem for elem in data if elem != target]

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Raymond Hettinger

@raymondh

6 years

If every core developer had to a periodically teach a series of Python courses to experienced engineers, perhaps #python development would become more user centric and there would be less of race to add arguably unnecessary complexity to the language.

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@raymondh

4 years

Welp, after one year of lockdown, today was the day it finally happened. I left my microphone unmuted during a 10 minute break in a #Python training course. So now a whole class heard me sing Willie Nelson's, ”Good hearted woman” to my wife. 😲 #lockdownfail #hotmike

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@raymondh

4 years

Thought for the day: The Python language, standard library, and ecosystem are so large that all users, even core developers and book authors, must content themselves with only knowing a fraction of it.

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Raymond Hettinger

@raymondh

6 years

#python news: Python 3.7 has been released! Guaranteed dict ordering, Dataclasses, Context variables and more.

Python Release Python 3.7.0

The official home of the Python Programming Language

www.python.org

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Raymond Hettinger

@raymondh

3 years

#Python tip: The list.insert() method can add elements one at a time, but slicing can more clearly and efficiently insert multiple elements at a time. >>> s = ['three', 'four', 'five'] >>> s[0:0] = ['one', 'two'] >>> s ['one', 'two', 'three', 'four', 'five']

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@raymondh

5 years

#Python 3.8 news: The typing module now makes it possible to annotate non-homogenous dictionaries: >>> class Person(TypedDict): name : str age : int >>> p = Person(name='matthew', age=10) >>> p {'name': 'matthew', 'age': 10}

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@raymondh

5 years

#Python humor with a message

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@raymondh

4 years

My advice on learning new #Python features: Don't approach it from the "I like it" or "I don't like it" point of view. Once approved, it is just a fact of life, neither good nor bad. Learn it deeply and see where it fits or doesn't fit in your life. Then use as needed. 🙂

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Raymond Hettinger

@raymondh

7 years

Dear computer book publishers, please DON'T USE SMART QUOTES in code! >>> print(“hello”) # bad >>> print("hello") # good

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@raymondh

5 years

Another interesting use of #python 's walrus operator is to compute differences between successive values in a data stream. This is the inverse of accumulate(): >>> data = [10, 14, 34, 49, 70, 77] >>> prev = 0; [-prev + (prev := x) for x in data] [10, 4, 20, 15, 21, 7]

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@raymondh

5 years

#Python tip: The any() and all() builtins have short-circuiting behavior, but that is lost if you use a list comprehension: all( for interface in interfaces) # Good all([ for interface in interfaces]) # Not so good

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@raymondh

6 years

#python 3.8 news: The second alpha release out today. Please try it out. One major feature that we've needed for a long time is shared memory for multiprocessing. Our story for multi-core just got a lot better ;-) Thank you Davin Potts!

Python Release Python 3.8.0a2

The official home of the Python Programming Language

www.python.org

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@raymondh

5 years

The #python walrus operator can be used to accumulate data: >>> data = [10, 4, 20, 15, 21, 7] >>> c=0; [(c := c + x) for x in data] [10, 14, 34, 49, 70, 77] How long before someone proposes in-place variants? [(c :+= x) for x in data]

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Raymond Hettinger

@raymondh

5 years

My editor has an interesting bug. Every few years, the font size gets larger.

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@raymondh

6 years

Great #Python news: Roman numeral literals! >>> 4 == IV True >>> XII + III == XV True

PEP 313 – Adding Roman Numeral Literals to Python | peps.python.org

This PEP (also known as PEP CCCXIII) proposes adding Roman numerals as a literal type. It also proposes the new built-in function “roman”, which converts an object to an integer, then converts the...

peps.python.org

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Raymond Hettinger

@raymondh

4 years

1/ #Python tip: The functools.cache() decorator is astonishingly fast. Even an empty function that returns None can be sped-up by caching it. 🤨

functools — Higher-order functions and operations on callable objects

Source code: Lib/functools.py The functools module is for higher-order functions: functions that act on or return other functions. In general, any callable object can be treated as a function for t...

docs.python.org

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@raymondh

3 years

#Python tip: Don't unnecessarily prefix function names with "get". In the sys module, getsizeof() should have been named sizeof(). The "get" is useless baggage.

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@raymondh

5 years

#python tip: itertools.repeat() is faster than range() for looping a fixed number of times when you don't need the loop variable. min(random() for i in range(10_000)) # 1.03 msec per loop min(random() for _ in repeat(None, 10_000)) # 841 usec per loop

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@raymondh

4 years

#Python assignment targets are remarkably general, even in cases where they don't make much sense. >>> s = [10, 20] >>> for s[0] in range(5): ... print(s) ... [0, 20] [1, 20] [2, 20] [3, 20] [4, 20]

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@raymondh

7 years

#python tip: Now that regular dicts retain insertion order, the fastest way to eliminate hashable duplicates while retaining order is: >>> list(dict.fromkeys('abracadabra')) ['a', 'b', 'r', 'c', 'd']

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@raymondh

5 years

#Python 's alternative increment operator is affectionately known as the space-invader operator. >>> score = 10 >>> score -=- 1 >>> score 11

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@raymondh

3 years

Relatively unknown #Python function that everyone needs sooner or later: textwrap.dedent(). This gem removes the common leading whitespace from indented multiline strings.

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@raymondh

5 years

#Python news: Tomorrow, we'll hit 200,000 packages in the #PyPI the package index. We have a rich ecosystem that doubled in size in a little over 2½ years. The 100,000 mark was on March 4, 2017:

Raymond Hettinger

@raymondh

8 years

#Python 's #Pypi package index just hit 100,000 packages. This is a major milestone and a sign of strong growth.

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@raymondh

4 years

#Python news: The video is up for my #PyConEstonia keynote: "Object Oriented Programming from scratch (four times)" Hope this expands your world view. Enjoy!

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@raymondh

6 years

#Python 3.8 news: We now have a Euclidean distance function in the math math module :-) Now, k-nearest neighbors boils down to: nsmallest(k, training_data, partial(dist, new_point))

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@raymondh

2 years

Today is my first day to teach #Python with version 3.11. The improved error messages are a real joy. When the final release happens, likely later today, do yourself a favor and upgrade immediately. It is mostly better, faster, and stronger but doesn't cost $6 million dollars.

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Raymond Hettinger

@raymondh

8 years

#python3 .6 news: OrderedDict is dead. Long live dicts that are ordered. Regular dicts are ordered and more compact:

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@raymondh

4 years

#Python tip: Database queries are especially fast if you copy the database into RAM: import sqlite3 source = sqlite3.connect('main_database.db') dest = sqlite3.connect(':memory:') source.backup(dest)

sqlite3 — DB-API 2.0 interface for SQLite databases

Source code: Lib/sqlite3/ SQLite is a C library that provides a lightweight disk-based database that doesn’t require a separate server process and allows accessing the database using a nonstandard ...

docs.python.org

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@raymondh

4 years

#Python tip: Adding __slots__ to a class is the easiest optimization you will ever do. * Faster instantiation: c=C() * Faster attribute reads and writes: c.x=1 * Smaller object size * Makes compiled language people happy (Java and C++ classes declare attributes up front)

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@raymondh

6 years

#python tip: __slots__ is underappreciated * Declares attributes upfront for readability * Saves significant space * Speeds up attribute access * Detects misspelled assignments It has a somewhat high payoff for so little work invested

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@raymondh

3 years

#Python news: It was always awkward to write a type annotation for methods that returned self (an instance of the current class). As of yesterday, typing.Self was added to make this much easier and more readable. It is a big win. 1/

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@raymondh

4 years

#python factlet: My parents were wrong. Two wrongs do make a right 😉 >>> two_wrongs = [False, False] >>> bool(two_wrongs) True

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@raymondh

4 years

#python tip: To update a list in-place, use a slice-assignment t = s ... s[:] = [f(x) for x in s if c(x)] Now, both "s" and "t" reflect the new data.

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@raymondh

7 years

#python tip: Concatenating a series of lists has quadratic performance. Use itertools.chain() or chain.from_iterable() instead.

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@raymondh

6 years

#Python news: Guido accepted PEP 572. Python now has assignment expressions. if (match := (data)) is not None: print((1)) filtered_data = [y for x in data if (y := f(x)) is not None]

PEP 572 – Assignment Expressions | peps.python.org

This is a proposal for creating a way to assign to variables within an expression using the notation NAME := expr.

peps.python.org

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@raymondh

7 years

#python list comparison techniques: # identity matters a is b # order matters; duplicates matter a == b # order ignored; duplicates matter Counter(a) == Counter(b) # both order and duplicates ignored set(a) == set(b)

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@raymondh

4 years

#Python floating point ninja tip: Summation accuracy is improved when terms are arranged in order of increasing magnitude. Instead of: giant + large + medium + small + tiny Write: tiny + small + medium + large + giant

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@raymondh

5 years

Here's the video for my #PyBay2019 keynote, "The Mental Game of Python: 10 strategies for managing complexity." Skip the intro. The meat starts at 2:40. There is only 1 slide with all 10 techniques. The rest is live coding with non-trivial examples.

The Mental Game of Python - Raymond Hettinger

This talk was presented at PyBay2019 - 4th annual Bay Area Regional Python conference. See pybay.com for more details about PyBay and click SHOW MORE for mor...

www.youtube.com

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@raymondh

7 years

#python tip: How do you combine a list of lists into a single set? >>> lol = [['a', 'b', 'c'], ['b', 'c', 'd'], ['d', 'e']] >>> set().union(*lol) set(['a', 'c', 'b', 'e', 'd'])

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@raymondh

6 years

#python tip: f-strings parsing is smart enough to handle named unicode code points :-) >>> ordinal, state = 50, "Hawaiʻi" >>> print(f'{ordinal} \N{long rightwards arrow} {state}') 50 ⟶ Hawaiʻi

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@raymondh

5 years

Debugging is the step where you take the bugs out. Programming is the step where you put them in ;-)

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@raymondh

4 years

#Python tip: Counters can easily be converted to and from regular dictionaries: >>> c = Counter(a=10, b=5) >>> d = dict(c) >>> d {'a': 10, 'b': 5} >>> Counter(d) Counter({'a': 10, 'b': 5}) Both directions use fast C code that copies the hash tables and updates ref counts.

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@raymondh

4 years

According to #Python 's datetime module, I am 20,454 days old today. My birthday plans include sheltering in place, eating a chocolate cupcake, and making an almost trivial commit to the random module.

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@raymondh

2 years

Here's a PDF for my #Python #PyConIT2022 talk: Structural Pattern Matching in the Real World: New tooling, real code, problems solved. This is intermediate and advanced level Structural Pattern Matching. tl;dr The “good stuff” is in section 1.2

PyITPatternMatchingTalk.pdf

Shared with Dropbox

www.dropbox.com

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@raymondh

6 years

Modern #Python lets you input and output large numbers in a much more human friendly way: >>> n = 1_234_567 >>> format(n, ',') '1,234,567'

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@raymondh

3 years

If you want to understand #Python 's global interpreter lock, I recommend this blog post. It is well written and well researched.

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@raymondh

3 years

#Python pop quiz: Is this code valid? If so, what does it do? def f(): yield 10 return 20 g = f() print(next(g)) print(next(g))

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@raymondh

5 years

#Python tip: None and NotImplemented are singletons. PEP 8 advises that comparisons for singletons should always be done with "is" or "is not", never the equality operators.

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@raymondh

5 years

#Python pop quiz. Do you know what this does: with open(False) as f: s = ()

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@raymondh

4 years

Am thinking of organizing a #StackOverflow conference. Any time two people start talking about something interesting, I'll have moderators break-up their group because similar conversations have happened before. 😉

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@raymondh

5 years

#Python wish: For the sake of users without command-line experience, tools like pip like should be runnable from within a Python interactive shell. The issue is particularly acute on Windows where finding executables and setting the path can be a challenge.

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@raymondh

4 years

Structural Pattern Matching is coming to #Python . The best way to learn about it is to reading the adventure game tutorial.

PEP 636 – Structural Pattern Matching: Tutorial | peps.python.org

This PEP is a tutorial for the pattern matching introduced by PEP 634.

peps.python.org

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@raymondh

4 years

The instructions for how to successfully use #Python 's super() has been my most successful bit of technical writing. It has had over a half-million readers. If if it were a book, it might have been a New York Times bestseller 🥴

Python’s super() considered super!

If you aren’t wowed by Python’s super() builtin, chances are you don’t really know what it is capable of doing or how to use it effectively. Much has been written about super() and much of that wri…

rhettinger.wordpress.com

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@raymondh

5 years

Playful #Python : class G: def __init__(self, s): self.s = s def __getattr__(self, t): return G(self.s + '.org') def __rmatmul__(self, other): return other + '@' + self.s fun, games = 'operator', G('tricks') print(fun @games .com)

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@raymondh

5 years

#Python 3.8 news: We now have a prod() function to complement the existing sum() function: >>> prior = 0.8 >>> likelihoods = [0.625, 0.84, 0.30] >>> (likelihoods, start=prior) 0.126

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@raymondh

4 years

#Python tip: To make a compound dictionary key where order doesn't matter, use frozenset(): color_mix = { frozenset({'red', 'yellow'}): 'orange', frozenset({'red', 'blue'}): 'purple', frozenset({'blue', 'yellow'}): 'green', frozenset({'red', 'blue', 'yellow'}): 'black', }

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@raymondh

10 months

#Python tip: Start 2024 right by mastering the itertools module. I recommend working through the itertool recipes one at a time until you understand how each of them work. After an hour or two, you will be an itertool boss.

itertools — Functions creating iterators for efficient looping

This module implements a number of iterator building blocks inspired by constructs from APL, Haskell, and SML. Each has been recast in a form suitable for Python. The module standardizes a core set...

docs.python.org

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@raymondh

4 years

#Python tip: Hard-coded constants should use the optional underscore as a thousands separator: >>> x = 1_234_567 Also, you can output numbers in that format: >>> f'{x:_d}' '1_234_567' Or with commas: >>> f'{x:,d}' '1,234,567' 1/

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@raymondh

4 years

1/ #Python factlet: random() gives you floats in the range 0.0 ≤ X < 1.0, but not all floats in that range are possible selections. For example, 0.05954861408025609 isn't a possible selection.

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@raymondh

1 year

#Python 3.12 factlet: There is a new itertool called batched() for grouping data into equal sized batches (with a possible odd lot at the end). Interestingly the corner cases of "batched(iterable, 1)" and "zip(iterable)" both give the same result.

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@raymondh

5 years

I learned something new today :-) Hyrum's Law: With a sufficient number of users of an API, it does not matter what you promise in the contract: all observable behaviors of your system will be depended on by somebody.

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@raymondh

4 years

StackOverflow is plagued by people who aggressively mark questions as duplicates. There are many distinct questions that happen to use the same library function in their answers. For example, I can think of many distinct and nuanced questions whose answer is itertool.product().

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@raymondh

4 years

Coming soon in #Python 3.10: A faster way to count bits in an integer: >>> x = 451 >>> bin(x) '0b111000011' >>> bin(x).count('1') # <-- old 5 >>> x.bit_count() # <-- new 5 1/

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Raymond Hettinger

@raymondh

5 years

#python tip: collections.Counter is a subclass of dict. As of Py3.6, dicts learned to remember insertion order. Consequently, counters are ordered as well. The most_common() method is like a stable sort on counts: >>> Counter('aaabccc').most_common(2) [('a', 3), ('c', 3)]

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Raymond Hettinger

@raymondh

6 years

#python3 tip: Numeric literals allow optional underscores to help improve readability: >>> trials = 1_000_000 >>> three_pi = 9.42477_79607 >>> avogadro = 6.022_140_857E+23

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Raymond Hettinger

@raymondh

4 years

Four ways to write all_equal(t) in #python : s[1:] == s[:-1] min(s) == max(s) # s must be non-empty g = itertools.groupby(s) next(g, True) and not next(g, False) all(map(operator.eq, s, itertools.islice(s, 1, None))) "Returns True if all the elements are equal to each other"

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Raymond Hettinger

@raymondh

3 years

#Python code review pop quiz: What does this code do? assert(0 <= i < len(s), 'index out of bounds')

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Raymond Hettinger

@raymondh

6 years

Good news: #Python 3 adoption continues to rise. Bad news: A lot of Python 2 users don't seem to know that the end is near (14 months left until Python 2 becomes completely unsupported).

Donald Stufft

@dstufft

6 years

Last month, 39.3% of downloads from PyPI were for Python 3 (excluding downloads where we don’t know what Python version they were for, like Mirrors, etc).

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Raymond Hettinger

@raymondh

4 years

#Python floating point ninja tip: Use parentheses to regroup sums to minimize accumulated round-off error. Instead of: a + b + c + d + e + f + g + h Write: ((a + b) + (c + d)) + ((e + f) + (g + h)) Note, the total work is unchanged.

Pairwise summation - Wikipedia

en.wikipedia.org

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Raymond Hettinger

@raymondh

6 years

#python tip: Q. How much code do you put in one statement? A. Statements should correspond to one complete thought expressible in a single sentence in plain English. English: I'll drive if it is raining; otherwise, I'll walk: Python: action = 'drive' if raining else 'walk'

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Raymond Hettinger

@raymondh

6 years

#Python 3.7 was just released. If you want a short tutorial on dataclasses, my Pycon talk will give you quick start:

Raymond Hettinger - Dataclasses: The code generator to end all code...

Speaker: Raymond HettingerThe PEP 557 dataclasses module is available in starting in Python 3.7. It will become an essential part of every Python programme...

www.youtube.com

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Raymond Hettinger

@raymondh

4 years

#Python regex tip: Alternations are tested left-to-right and the first match wins. So, put the longer matches first to avoid aliasing shorter alternatives: >>> re.findall(r'<|>|<=|>=', '3 <= 4') # Incorrect ['<'] >>> re.findall(r'<=|>=|<|>', '3 <= 4') # Correct ['<=']

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Raymond Hettinger

@raymondh

4 years

What tool in #Python amazes you that it can even be possible? For me, () gives a fresh sense of wonder every time I use it.

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Raymond Hettinger

@raymondh

6 years

#Python 2.7 news: Winter is coming.

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