The configuration might not come directly from a JSON file—for example, - it might be embedded in a larger file or generated by anothe prrogram—so + it might be embedded in a larger file or generated by another program—so we should modify the constructor to take the loaded JSON configuration as input.
Section 3.1: Getting Started
aaaaaaaaabbbbcSection 3.2: Hashing Files
but is it? As a more stringent test, let’s try hashing every line of text in -Project Gutenberg‘s version of the novel Dracula +the Project Gutenberg version of the novel Dracula and plot the distribution (Figure 3.3).
diff --git a/docs/finale/index.html b/docs/finale/index.html
index 0ebbc94f8..e1cf25f8b 100644
--- a/docs/finale/index.html
+++ b/docs/finale/index.html
@@ -345,7 +345,8 @@ Chapter 27: Conclusion
Consider the bicycle–more specifically, +
Consider the bicycle: +more specifically, the De Rosa SK Pininfarina (Figure 27.1). I think it’s beautiful, but I wouldn’t call it art, diff --git a/docs/intro/index.html b/docs/intro/index.html index 0a5d45b3c..f53e64d70 100644 --- a/docs/intro/index.html +++ b/docs/intro/index.html @@ -559,7 +559,7 @@
Section 1.6: Acknowledgments
This one’s for Mike and Jon:
- I’m glad you always found time to chat.
Chapter 24: Undo and Redo
we will also implement undo, which will introduce another commonly-used software design pattern.Section 24.1: Getting Started
-Our file fiewer has four classes (Figure 24.1):
+Our file viewer has four classes (Figure 24.1):
-
A
@@ -753,7 +753,7 @@Windowcan draw lines and report its size.Section 24.3: Going Backward
so we are essentially undoing our undo forever. The solution is to modify the base classActionto have a.savemethod that tells the application whether or not to save this action. -The default implemenation returnsTrue, +The default implementation returnsTrue, but we override it inUndoto returnFalse:class Undo(Action): diff --git a/info/bibliography.bib b/info/bibliography.bib index b79b872e1..e9c4d346a 100644 --- a/info/bibliography.bib +++ b/info/bibliography.bib @@ -29,7 +29,7 @@ @book{Brand1995 @book{Bentley1982, author = {Jon Louis Bentley}, title = {Writing Efficient Programs}, - publisher = {Prentice Hall {PTR}}, + publisher = {Prentice-Hall {PTR}}, year = {1982}, isbn = {978-0139702440} } diff --git a/info/glossary.yml b/info/glossary.yml index 5f1bd770a..c37b31a0a 100644 --- a/info/glossary.yml +++ b/info/glossary.yml @@ -22,7 +22,7 @@ en: term: abstract base class def: > - An [abstract_class](#abstract_class) from which the [class](#class) + An [abstract class](#abstract_class) from which the [class](#class) in question is derived. - key: abstract_class @@ -1427,7 +1427,7 @@ full : JavaScript Object Notation def: > A way to represent data by combining basic values like numbers and - character strings in [lists](#list) and [key/value](#dictionary) + character strings in [lists](#list) and [key-value](#dictionary) structures. The acronym stands for "JavaScript Object Notation"; unlike better-defined standards like [XML](#xml), it is unencumbered by a syntax for comments or ways to define a [schema](#schema). diff --git a/info/wordlist.txt b/info/wordlist.txt index 404dd1683..c4c442b03 100644 --- a/info/wordlist.txt +++ b/info/wordlist.txt @@ -1,333 +1,619 @@ -ABCDEF -ACM -AST -Andreas -Aniche -Bitwise -Breakpoint -Buildability -CPUs -CSV -CTAN -CamelCase -Connor -Cryptographic -Ctrl -DNS -DOM -Dataframes -De -Docstrings -EJS -Enforceability -Extensibility -Filesystem -Fortran -Fucci -Gitlet -Globals -Globbing -Glosario -GrandChild -Harrelson's -Hermans -Hoye -HyperText -JSON -Kamin -Kerievsky -Kernighan -Kohavi -LaTeX -LeftChild -Licensor -Licensor's -Lifecycle -Linearize -Linters -Liskov -Loewy -Lorgat -Lorgat's -MERCHANTABILITY -Matcher -Maël -Meszaros -Mixin -NONINFRINGEMENT -Nison -Nison's -NonCommercial -Nystrom -Nystrom's -OLAP -OLTP -Oram -PNG -Panchekha -Pavel -Petre -PicoSAT -Pininfarina -Polge -Polge's -Polymorphism -Pre -Prover -Pythonic -Recurse -Reim's -Reimplemented -Reproducibility -RightChild -Runtime -Ruten's -SHA -SIGSOFT's -SVG -Schon -Sinel -Snakemake -TCP -TLL -Teardown -Templated -Thibault -Tichy -Tokenize -Tokenizer -Tokenizing -UTF -Unix's -Unsatisfiable -VM -VM's -Wasim -Watchpoints -YAML -Yim -Zeller's -aaa -abc -abcx +16-bit +1970s +19th +2-digit +2000s +20th +256-bit +2nd +3-bit +32-bit +4-letter +4.anything +4k +64-bit +64-character +64k +7-bit +8-bit +acknowledgments acyclic -analytics -andreas -aosa +addison-wesley +adilov +affordance +affordances +akand +alexapolsky +alexey +aliased +aliasing +all-in-one-file +alvee +andré +andrén +aniche +annotating +ansi api +apis +apparently-random +append +appending +appends +application-specific archiver archivers -ast -attr -attrs -bb -beq +arpan +as-is +as-yet-unwritten +ascii +assembler +asynchronous +ats +auto-completion +automating +bacchelli +backspace-delete +backward-compatible +bahman +base-10 +base-16 +bellini +better-defined +bibliography +bidirectional +big-endian +big-oh bitwise -blockcol +block-based +boole +boolean breakpoint +breakpoints +browser-based +browsers brubeck +brute-force +buildability +buildable +built-in +built-ins +burak bytecode -cProfile -chainmap -chris -christopher -clarkes -classdef -cls -combinatorial +callable +callout +camelcase +canino +chunking +circularity +client-server +closely-related +co-author +co-founder +column-wise +comma-separated +command-line +commonly-used +compaction +compacts compatibilities +compilers composable -config -connor -contrib -cprofile -cryptographic +concatenate +concatenates +concatenating +conditionals +conery +correa +cpus +crc +cross-references +cs csv ctan -data's +ctrl-c +ctrl-x +currently-visible +curses-based dataframe -dataframe's dataframes +dataset datasets datatypes -debugger's -dep -derosa -df -dir +davide +debugger +debuggers +decrement +delete-in-place +denominators +dependencies +depth-first +devanagari +dibernardo +dictionary-based +dictionary-like +difficult-to-debug disassembler disassemblers +disassembles dns +do-nothing docstring docstrings -dom -dracula -dup +dominguez +double-precision +double-quoted +dozenth +drumm +dynamically +e-book +ece ejs -elif -else's -encodings +end-of-line endian -eniac -env -eq -evans +endpoint +enforceability +enumeration +equivalently +error-handling +error-prone +ever-larger +ex-or +exception-based +exclusions expander exponentiality -expr extensibility +extensible +falsy +faq +felienne +file-backed +filename +filenames filesystem +filesystems +firas +fixed-size fixme -fs -fullwidth -func -funcobj -funcs +flake8 +floating-point +flowchart +fortran +four-digit +four-part +frameworks +fraser +fucci +full-featured +fully-functional +general-purpose +genever +github gitlet globals globbing glosario +gnu +gorcenski gutenberg +guyer +gvwilson +hand-written +harassment-free harrelson -hashlib +hashes +hashing-based hennessy -hippocratic +hermans +high-level +higher-level +histogram +hoek +hostname +hostnames hoye html +html-like +html5 http -img -init -interp -io -ip +human-readable +hypertext +hyphens +ieee +implementations +in-memory +incremented +infix +initializes +insertable +installable +instantiated +instantiates +insulting/derogatory +inter-package +interactively +interchangeably +interleaving +internally-generated +interoperability +interpreter-based +introspect +invalidation +invalidity +isbn isort +iterating +iterator +iterators itertools -jekyll -joseph -jpg +javascript json -julia -len +juanan +juristo +just-in-time +kamin +karimi +karlton +kaufmann +kerievsky +kernighan +key-to-sequence +key-value +keystroke-processing +kilobyte +knock-on +kohavi +landy +large-scale +left-to-right +lexical +licensee licensor -lifecycle +line-wrapping +linearize linter linters +linting liskov +literals +little-endian loewy +log-structured +long-lived +lookup-and-call lorgat -mael -marthas -mary +low-level +lower-case +lower-level +machine-readable +made-up +mahmoodur +maintainable +maintainers +mantissa +markdown +markku +mass-produced matcher matchers -methoddef -michael +maurício +maël +mccloy +mcgraw-hill +mejia +memory-to-memory +merchantability +meszaros +micro-steps mimetypes -mis +mini-language +mini-languages +miras mixin -multibyte -multiline -multiway -mx -nc -ncol +modulo +moosvi +multi-bit +multi-byte +multi-dimensional +multi-file +multi-letter +multi-part +multi-site +multi-way +mutually-compatible +name-to-class +name-value +naming-at-creation +new-and-improved +newline +newlines +newly-created +ng +nisan nison -nrow -num +no-one +noam +non-commercial +non-compliance +non-empty +non-interactive +non-latin +non-negative +non-text +non-zero +noninfringement +now-familiar +numerators nystrom +object-oriented +off-by-one +oivo +okamoto olap oltp -oop -paige +one-byte +one-dimensional +one-line +one-off +open-closed +operand +operands +optimizations +optionally +or'd +oram +orderings +out-of-date panchekha -param +parent-child +parsed +parser parsers -patterson -pavel -perf +parses +part-way +partially-completed +partially-formed +partially-generated +pass-fail-error +pereira persistable +petre pexpect php picosat +pininfarina +pipe-and-filter +placeholders +platform-independent +plauger +plos +plug-in +png +png-formatted +point-to-point +polge polymorphism -profiler +portability +post-condition +post-conditions +postfix +pothole_case +pre-commit +pre-condition +pre-conditions +pre-existing +precisely-formatted +predefined +prentice-hall +previously-injected +previously-read +printable +production-quality +properly-nested +prototyping prover -prover's provers -prr -py +pseudo-random +ptr pyfakefs pytest +python-specific pythonic -quadruply -raymond +quadruply-nested +quick-fix +rahman +re-add +re-create +re-creates +re-defining +re-draw +re-match +re-represent +re-run +re-set +re-think +re-use +re-used +re-uses +re-using +re-write +real-world +recalculation +recently-accessed +recompile recurse recursing +recursion +recursively +red-green-blue +redefinition +refactor +refactored +refactoring refactorings +regex +regexp +register-to-register reim reimplemented -repo +renames +reproducibility +reproducible resizeable -roundtrip +resizing +result—typing +right-to-left +rightchild +roundoff +row-oriented +row-wise +run-time runnable runtime ruten -satisfiable -semver -sexualized -sha +saibene +sarkar +scalene +scanniello +schema +schocken +self-closing +self-referential +self-taught +semantic-version +sha-256 +shareable +sheena +shepperd +shimon +sigsoft +sigweni sinel -smt +single-argument +single-byte +single-letter +single-process +single-record +single-step +single-stepping +single-variable +singleton snakemake +socorro +special-purpose +specially-named +specifiers +sql sqlite -sqrt -stmt +square-specific +stack-handling storable straightfoward +strictly-typed +struct +sub-directories +sub-expressions +sub-keys +sub-list +sub-lists +sub-patterns sublicense substrings +subtracts +superceded svg -tcp -tcpip -tdd +tabular +tavish +tcp/ip +teardown +templated templating -testability's +test-driven +testability +testable textwrap -th +thermocouple +three-bit +tichy +time-consuming +timestamped +timestamps +timezone tll -toctou -tok tokenization tokenize tokenizer tokenizing -topo +tool-based +top-down +top-level +top-most +top-to-bottom tradeoffs +traversal +triply-nested +truncating truthy -txt -udhr +tuple +turhan +turnator +two-digit +two-dimensional +two-element +two-part +unaccented +unaddressed unenforceability +unenforceable unfittable -ungc unicode +unimaginatively unix +unmaintainable +unpacks unparse +unsurprisingly upcall upcalling -url -urlparse +upcalls +upper-case +upper-left +user-defined +user-level +user-specified utc -utf -util +utf-32 +utf-8 +uyaguari validator -varargs +variable-length +versioning +viewable viewport +vlissides vm -wasim +vms watchpoint watchpoints -webaim +well-defined +well-designed +well-known +widely-used +wildcards +windowing +workflows wrappable +write-only +xml +xor +xunit yaml -yml +yanina +yes-or-no +yim +yundong +z-buffering +z3 zeller +zines diff --git a/lib/mccole/bin/post_spellcheck.py b/lib/mccole/bin/post_spellcheck.py deleted file mode 100644 index 2ed4b59c5..000000000 --- a/lib/mccole/bin/post_spellcheck.py +++ /dev/null @@ -1,28 +0,0 @@ -#!/usr/bin/env python - -"""Compare standard input words to known words.""" - - -import sys - - -def main(wordlist): - """Main driver.""" - actual = {x.strip() for x in sys.stdin.readlines()} - with open(wordlist, "r") as reader: - expected = {x.strip() for x in reader.readlines()} - report("unknown", actual - expected) - report("unused", expected - actual) - - -def report(title, words): - """Report a set of words.""" - if not words: - return - print(f"# {title}") - for w in sorted(words): - print(w) - - -if __name__ == "__main__": - main(sys.argv[1]) diff --git a/lib/mccole/bin/pre_spellcheck.py b/lib/mccole/bin/pre_spellcheck.py deleted file mode 100644 index 0bd323ee8..000000000 --- a/lib/mccole/bin/pre_spellcheck.py +++ /dev/null @@ -1,40 +0,0 @@ -#!/usr/bin/env python - -"""Remove code and math before spell-checking.""" - - -import argparse - -import util -from bs4 import BeautifulSoup -from markdown import markdown - - -def main(): - options = parse_args() - handle(options.pages, expand) - handle(options.slides, expand) - - -def expand(text): - return markdown(text, extensions=["md_in_html"]) - - -def handle(filenames, pre_processor=None): - for f in filenames: - with open(f, "r") as reader: - text = reader.read() - if pre_processor is not None: - text = pre_processor(text) - print(util.cleanup_html(BeautifulSoup(text, "html.parser"))) - - -def parse_args(): - parser = argparse.ArgumentParser() - parser.add_argument("--pages", nargs="+", default=[], help="pages") - parser.add_argument("--slides", nargs="+", default=[], help="slides") - return parser.parse_args() - - -if __name__ == "__main__": - main() diff --git a/lib/mccole/bin/spelling.py b/lib/mccole/bin/spelling.py new file mode 100644 index 000000000..7e95ec4e0 --- /dev/null +++ b/lib/mccole/bin/spelling.py @@ -0,0 +1,93 @@ +"""Produce or check consolidated vocabulary.""" + +import argparse +from markdown import markdown +from pathlib import Path +import re +import string +import sys +from bs4 import BeautifulSoup +from spellchecker import SpellChecker +import util + +PAT_DOC = [ + (re.compile(r'^\\\(.+?\\\)'), " "), + (re.compile(r'[–—]'), " "), +] +PAT_WORD = [ + (re.compile(r'^[“”’‘…\(\)#]*'), ""), + (re.compile(r'[“”’‘…,\?\.:;\(\)°%]*$'), ""), + (re.compile(r'’s'), ""), + (re.compile(r'^(0x)?[\(\)\d\.×\+/–-]+$'), ""), + (re.compile(r'’'), "'"), +] + + +def main(): + """Main driver.""" + options = parse_args() + config = util.load_config(options.config) + extra_words = get_extra_words(options) + docs = read_docs(options, config) + words = extract_words(docs) + checker = SpellChecker() + unknown = checker.unknown(words) - extra_words + for word in sorted(unknown): + print(word) + + +def extract_words(docs): + """Extract set of all words from documents.""" + words = set() + for doc in docs: + text = normalize(doc.text, PAT_DOC) + words |= {normalize(w, PAT_WORD) for w in doc.text.split()} + return words + + +def get_extra_words(options): + """Load list of extra known words.""" + if not options.extra: + return set() + with open(options.extra, "r") as reader: + return {word.strip() for word in reader.readlines()} + + +def normalize(text, patterns): + """Create normalized form of text.""" + for (pat, replacement) in patterns: + text = pat.sub(replacement, text) + return text + + +def parse_args(): + """Parse arguments.""" + parser = argparse.ArgumentParser() + parser.add_argument("--config", required=True, help="Configuration file") + parser.add_argument("--extra", help="File containing list of extra known words") + parser.add_argument("--slides", default=False, action="store_true", help="Process slides") + return parser.parse_args() + + +def read_docs(options, config): + """Read all HTML documents.""" + result = [_read_doc(Path(config.out_dir, "index.html"), "main")] + for slug in [*config.chapters, *config.appendices]: + result.append(_read_doc(Path(config.out_dir, slug, "index.html"), "main")) + if options.slides: + for slug in config.chapters: + result.append(_read_doc(Path(config.out_dir, slug, "slides", "index.html"), "body")) + return result + + +def _read_doc(filename, root): + """Read a single HTML document.""" + with open(filename, "r") as reader: + text = reader.read() + text = markdown(text, extensions=["md_in_html"]) + soup = BeautifulSoup(text, "html.parser").find(root) + return util.cleanup_html(soup, bib=True) + + +if __name__ == "__main__": + main() diff --git a/lib/mccole/mccole.mk b/lib/mccole/mccole.mk index c7d16c750..e4d76fd28 100644 --- a/lib/mccole/mccole.mk +++ b/lib/mccole/mccole.mk @@ -109,16 +109,7 @@ fonts: ## spelling: check spelling against known words .PHONY: spelling spelling: - @make wordlist \ - | python ${MCCOLE}/bin/post_spellcheck.py ${ROOT}/info/wordlist.txt - -## wordlist: make a list of unknown and unused words -.PHONY: wordlist -wordlist: ${ROOT}/docs/index.html - @python ${MCCOLE}/bin/pre_spellcheck.py --pages ${SRC_PAGES} --slides ${SRC_SLIDES} \ - | aspell -H list \ - | sort \ - | uniq + @python ${MCCOLE}/bin/spelling.py --config ${ROOT}/config.py --extra info/wordlist.txt ## index: show all index entries .PHONY: index diff --git a/src/binary/index.md b/src/binary/index.md index 2cf70ee37..6f0a5f796 100644 --- a/src/binary/index.md +++ b/src/binary/index.md @@ -118,7 +118,7 @@ putting it another way, Finally, `~` flips its argument: 1 becomes 0, and 0 becomes 1. -When these operators are used on multibit values +When these operators are used on multi-bit values they work on corresponding bits independently as shown in [%t binary-ops %].diff --git a/src/build/index.md b/src/build/index.md index 518fcaa78..790ca5297 100644 --- a/src/build/index.md +++ b/src/build/index.md @@ -176,7 +176,7 @@ Our implementation works, but we can do better: 1. The configuration might not come directly from a JSON file—for example, - it might be embedded in a larger file or generated by anothe prrogram—so + it might be embedded in a larger file or generated by another program—so we should modify the constructor to take the loaded JSON configuration as input. 2. Printing actions to the screen isn't very useful, diff --git a/src/dup/index.md b/src/dup/index.md index 3b75e787b..7042100f7 100644 --- a/src/dup/index.md +++ b/src/dup/index.md @@ -49,7 +49,7 @@ we create a `tests` directory with six files: | `a1.txt` | `a2.txt` | `a3.txt` | `b1.txt` | `b2.txt` | `c1.txt` | | ---- | ---- | ---- | ---- | ---- | ---- | -| aaa | aaa | aaa | bb | bb | c | +| `aaa` | `aaa` | `aaa` | `bb` | `bb` | `c` | We expect the three `a` files and the two `b` files to be reported as duplicates. There's no particular reason for these tests—we just have to start somewhere. @@ -124,7 +124,7 @@ The output seems random, but is it? As a more stringent test, let's try hashing every line of text in -[Project Gutenberg][gutenberg]'s version of the novel *Dracula* +the [Project Gutenberg][gutenberg] version of the novel *Dracula* and plot the distribution ([%f dup-naive-dracula %]). [% figure @@ -193,7 +193,7 @@ other than generating random strings of bytes and hashing them. Cryptographic hash functions are hard to write—or rather, it's very hard to prove that a particular algorithm has the properties we require. We will therefore use a function from Python's [hashing library][py_hashlib] -that implements the [%g sha256 "SHA256" %] algorithm. +that implements the [%g sha256 "SHA-256" %] algorithm. Given some bytes as input, this function produces a 256-bit hash, which is normally written as a 64-character [%g hexadecimal "hexadecimal" %] string. @@ -290,9 +290,9 @@ What are the actual odds? - Why do `hash(123)` and `hash("123")` work but `hash([123])` raise an exception? -### How Good Is SHA256? {: .exercise} +### How Good Is SHA-256? {: .exercise} -- Write a function that calculate the SHA256 hash code +- Write a function that calculate the SHA-256 hash code of each unique line of a text file. - Convert the hex digests of those hash codes to integers. diff --git a/src/finale/index.md b/src/finale/index.md index 4f5ea2d69..6966d4f27 100644 --- a/src/finale/index.md +++ b/src/finale/index.md @@ -5,7 +5,8 @@ caption="De Rosa SK Pininfarina bicycle." %] -Consider the bicycle–more specifically, +Consider the bicycle: +more specifically, the De Rosa SK Pininfarina ([%f finale-bicycle %]). I think it's beautiful, but I wouldn't call it art, diff --git a/src/ftp/index.md b/src/ftp/index.md index 41afe8baa..597a8d196 100644 --- a/src/ftp/index.md +++ b/src/ftp/index.md @@ -104,8 +104,8 @@ when we run the client and server in separate terminal windows. [% figure slug="ftp-interaction" img="interaction.svg" - alt="Client/server interaction" - caption="Steps and messages in client/server interaction." + alt="Client-server interaction" + caption="Steps and messages in client-server interaction." %] There's a *lot* going on here, diff --git a/src/intro/index.md b/src/intro/index.md index ce457ef57..2a142611f 100644 --- a/src/intro/index.md +++ b/src/intro/index.md @@ -129,7 +129,7 @@ All of the written material in this book is licensed under the [Creative Commons - Attribution - NonCommercial 4.0 International license][cc_by_nc] (CC-BY-NC-4.0), while the software is covered by the [Hippocratic License][hippocratic_license]. -The first license allows you to use and remix this material for non-commercial purposes, +The first license allows you to use and remix this material for noncommercial purposes, as-is or in adapted form, provided you cite its original source; if you want to sell copies or make money from this material in any other way, @@ -207,5 +207,5 @@ we all get a lot.*This one's for Mike and Jon:*diff --git a/src/intro/syllabus_linear.svg b/src/intro/syllabus_linear.svg index a8ca291f5..55d13c522 100644 --- a/src/intro/syllabus_linear.svg +++ b/src/intro/syllabus_linear.svg @@ -76,7 +76,7 @@
- *I'm glad you always found time to chat.* + *I am glad you always found time to chat.*Archiver -+ dup->archive @@ -99,7 +99,7 @@ + glob->archive @@ -192,7 +192,7 @@ Machine + interp->vm @@ -209,7 +209,7 @@ + mock->archive @@ -353,7 +353,7 @@ + binary->vm @@ -442,7 +442,7 @@ A Debugger + viewer->debugger @@ -453,7 +453,7 @@ + vm->debugger diff --git a/src/intro/syllabus_regular.svg b/src/intro/syllabus_regular.svg index 487b70d09..19220fb7a 100644 --- a/src/intro/syllabus_regular.svg +++ b/src/intro/syllabus_regular.svg @@ -59,7 +59,7 @@ Archiver + dup->archive @@ -84,7 +84,7 @@ + glob->archive @@ -162,7 +162,7 @@ Machine + interp->vm @@ -174,7 +174,7 @@ + mock->archive @@ -273,7 +273,7 @@ + binary->vm @@ -332,13 +332,13 @@ A Debugger + viewer->debugger + vm->debugger diff --git a/src/persist/index.md b/src/persist/index.md index eafc33d8a..5802e1875 100644 --- a/src/persist/index.md +++ b/src/persist/index.md @@ -182,7 +182,7 @@ we can follow the Open-Closed Principle by rewriting our functions as classes. We will also use [%i "dynamic dispatch" %][%/i%] as we did in [%x interp %] to handle each item -so that we don't have to modify a multiway `if` statement +so that we don't have to modify a multi-way `if` statement each time we add a new capability. The core of our saving class is: diff --git a/src/undo/index.md b/src/undo/index.md index 64ea3d75f..daec80d6c 100644 --- a/src/undo/index.md +++ b/src/undo/index.md @@ -15,7 +15,7 @@ which will introduce another commonly-used software design pattern. ## Getting Started {: #undo-start} -Our file fiewer has four classes ([%f undo-classes %]): +Our file viewer has four classes ([%f undo-classes %]): - A `Window` can draw lines and report its size. @@ -239,7 +239,7 @@ we are appending the action to the history before doing the action, so we are essentially undoing our undo forever. The solution is to modify the base class `Action` to have a `.save` method that tells the application whether or not to save this action. -The default implemenation returns `True`, +The default implementation returns `True`, but we override it in `Undo` to return `False`: [% inc file="undoable.py" keep="Undo" %]