Python script, ASCII text executable
Style Guide for Python Code in the roundabout project
This document provides conventions for the coding style used in the Roundabout project. Rules can be broken -- just try to make the code as readable as you can.
Code should be written for Python 3.10 unless I say otherwise.
When something is not covered by this document, refer to PEP 8. However, please read this even if you know PEP 8, as it diverges in some places.
Code Layout
Indents and Line Continuation
Keep lines up to 80 characters long. Use 4 spaces for indentation, per level. Do not use tabs, and do not put trailing whitespace.
For parentheses, three styles are accepted:
# No indent.
thing = function(arg1, arg2)
# Hanging indent. Align to the contents, not to the bracket.
thing = function(arg1, arg2
arg3, arg4, arg5)
# Full indent. Here only one argument or variable or whatever is allowed per line.
# The closing bracket must be at the previous indent level.
# Any level is allowed, but it must be a multiple of 4.
thing = function(
arg1,
arg2,
arg3,
arg4
)
Collections should read like lists, not tables.
fruits = ["apple", "tomato", "pear", "cherry", "plum", "melon", "grape", "aubergine",] fruits = [ "apple", "tomato", "pear", "cherry", "plum", "melon", "grape", "aubergine", ] # Don't! fruits = [ "apple", "tomato", "pear", "cherry", "plum", "melon", "grape", "aubergine", ]
Additionally, for a collection meant to be expanded use a trailing comma.
For long expressions, begin the line with the operator and align the operand with the indentation level. This is not permitted by PEP 8, but it follows mathematics and leads to nicer layouts.
population = (population
+ births
+ immigrants
- deaths
- emigrants)
When the hanging indent could be mistaken for a block, add an empty line.
Backslashes are discouraged, but allowed if it is the only way to write your expression. For example:
really_long_variable_name_hopefully_yours_wont_be_as_long = \ "Really long value."
Blank Line Rules
Two between top-level class or function definitions.
One between local functions or methods.
One is allowed to separate related groups and logical sections.
One at the end of the file.
One below imports.
Imports
Imports should be on separate lines. from-imports must import all objects on the same line though.
import flask import os from models import User, Post
Imports should be ordered like this:
__future__statementsone blank line
magic names (
__all__,__version__)one blank line
library imports
library
from-importsone blank line
application imports
application
from-imports
Wildcard imports are discouraged and prohibited for libraries. However, they are fine if the module
defines __all__.
Interior Whitespace
Never insert more than one space around operators and other symbols. Never add spaces just to align lines.
When to use
around the lowest priority operators in an expression, comparisons, assignments, and logical operators, as well as the function annotation arrow
# Do thing += 10 + 2*thing # Don't thing+=10+2 * thing # Acceptable; use your best judgement thing += 10 + 2 * thing
after the colon when defining a single-line clause, or an annotation
after commas or semicolons
after the comment sign
#When to avoid
when passing keyword arguments or defining argument defaults, unless they are annotated
inside any brackets
# Do function(arg1, arg2) # Don't! function( arg1, arg2 )
after a trailing comma
# Do (0,) # Don't! (0, )
before commas, semicolons or colons
# Do x, y = y, x # Don't! x , y = y , x
around the slice operator
:before an argument list
# Do function(arg1, arg2) # Don't! function (arg1, arg2)
before the indexing operator
# Do dictionary["key"] = "Hello World!" # Don't! dictionary ["key"] = "Hello World!"
Other
Never use the semicolon for multiple statements; while allowed, it is discouraged as it hurts readability. Similarly discouraged are one-line clauses.
Strings
Only use double quotes like " for strings: single quotes are harder to spot, and they conflict with the common apostrophe.
For docstrings you should follow PEP 257. Additionally, docstrings should use Markdown to allow for a future tool to convert them to docs. HOWEVER arguments should be described using the ReST syntax, as it is more readable in the code. Other than this, they should be kept plaintext to prevent markup language battles (Python prefers RST, but most use Markdown).
Naming
Identifiers must only use ASCII characters. Abbreviations should be kept to a minimum and it should be
made sure that they are widely used and accepted already.
(id for identifier or repo for repository is acceptable, but avg for average is not). Generally, names should be easy to pronounce.
Class names must use UpperCamelCase with the first letter of each word capitalised and no underscores.
Other names (function, variable) should use snake_case with all words lowercase and separated by underscores.
For instance and class methods, only name the first argument self or cls, respectively.
To avoid conflicts, append an underscore or use a synonym but do not corrupt the spelling (class_ is better than clss or klass or classs or whatever).
Constants are an exception. They should use UPPER_CASE with underscores.
Non-public names should be prefixed with an underscore. In case it's really important to not use them, use a double underscore to invoke name mangling.
Comments
Block comments should be complete sentences; line comments don't need to. Write comments in
English and always use a space after the comment sign, as stated above, unless it's an UNIX
interpreter descriptor (#!) where you should not. Inside block comments, separate paragraphs
with an empty comment, like in Markdown. For a solo sentence, full stops are optional.
Avoid stating the obvious or contradicting the code.
Inline comments must be separated with more than one space from the statement, and they may be aligned.
In comments, never alter the case of identifiers, as it may lead to confusion.
Leaving TODO comments as personal notes is allowed, but they should be removed before merging or a release.
Programming
OOP Guidelines
Do not use getters and setters for class attributes. If you do need to change some other things, use properties.
Prefer overloading the operators; make using your objects as natural and Pythonic as possible.
Exceptions
Make exceptions specific enough, so catching them can be explicit.
Do not use the bare except clause. Make try clauses as short as possible to avoid silencing
unrelated bugs.
Other
Comparisons to singletons (True, False, None etc.) should be done with the identity operators
is and is not, not with the comparison operators. Use is not, not not ... is.
Unless it would be ambiguous, use the implicit truth test to check that numbers are different to 0, that containers have contents and similar tests.
Do not assign lambdas to identifiers. Make a real function instead.
Use with context managers to ensure resources are properly cleaned up.
Prefer making functions that take arguments and return a value instead of making them directly take global variables or process the information such as writing.
Use the methods startswith() and endswith() instead of string slicing to check for prefixes
or suffixes.
To compare types, use isinstance() instead of the is operator with type() (this is one of
my problems with Python, but it's the standard).
Use a proper condition for while instead of a while True that breaks.
Use for loops instead of while loops when possible, and use Pythonic iteration instead of
C-style iteration.
To call shells, use the subprocess module instead of os.system() and use the functions
that allow giving a list of arguments instead of a string, it leads to better security.
Similarly, avoid writing SQL manually, use Alchemy. If you must write SQL manually, be extra careful.
Jinja style guide
Jinja should be written like Python, with the following additions:
Tags should be written as {% <content> %} and expressions as {{ <content> }}. That is,
put spaces around the content.
Always indent tag contents, just like you would indent HTML tags! If a tag contains other tags and it wouldn't disrupt whitespace, you should indent the contents.
The filter operator | should have spaces around it, unless it's in a more complex expression
when it shouldn't.
Translations should always be done with the {% trans %} tag provided by Babel, not with
gettext(), _() or others. No exceptions.
The quoting rules are as in Python, unless it's in an HTML attribute, in which case you should use single quotes, as HTML takes precedence.
HTML style guide
HTML tags should be written in lowercase, with attributes in lowercase as well. Attribute values should be quoted with double quotes. Attribute minimisation is suggested for boolean attributes.
Always indent tag contents with 4 spaces, except in plaintext tags like pre or textarea, where
you should not indent.
The tag should be multiple lines if the content is complex. Otherwise, mirror the page layout.
IDs or classes should be written in kebab-case. Names should be written in snake_case to
provide better compatibility with Python.
Also, when making custom tags, always use a hyphen in the tag name, to make sure they won't be standardised in the future.
Event attributes are allowed as well, but please keep the JS inside shorter than 64 characters. If you need more make a function in a script tag or a separate file.
CSS style guide
CSS selectors, properties and values should be written in lowercase. Custom properties should be
written in kebab-case.
Always indent the contents of a ruleset with 4 spaces.
Unlike some other style guides, we do not require each selector after a comma to be on a new line. However, if they're too long, very complex or similar and they benefit from alignment, you should do so.
IDs are preferred over classes when the element only appears once on the page.
Tag selectors are allowed! Style the default widgets as you see fit, because it leads to
cleaner HTML. We also apply a reset stylesheet to make sure the default styles are consistent.
In what scenario would you want an unstyled button in your site? Never! Then why always use
<button class="btn btn-primary"> when it's the only kind of <button> your site has?
However, provide class-based alternatives for tag styles. For example, Efficient UI styles
button by default, but it also styles .button to allow hyperlinks or other elements to look
like buttons. Using both isn't needed though.
Also, selectors can be nested where it makes sense, however the > selector is preferred over
plain nesting, which is generally discouraged.
Use of fancy counters and data-attributes is allowed, but only for cosmetic purposes. We've got server-side templating, profit from it!
JavaScript style guide
JS should use double quotes for strings, and lowerCamelCase for names, and indenting should be 4 spaces. Otherwise I can't comment, because JS is ugly by nature.
1
Style Guide for Python Code in the roundabout project
2
=====================================================
3
This document provides conventions for the coding style used in the Roundabout project.
5
Rules can be broken -- just try to make the code as readable as you can.
6
Code should be written for Python 3.10 unless I say otherwise.
8
When something is not covered by this document, refer to [PEP 8](https://peps.python.org/pep-0008/).
10
However, please read this even if you know PEP 8, as it diverges in some places.
11
Code Layout
13
-----------
14
### Indents and Line Continuation
16
Keep lines up to 80 characters long. Use 4 spaces for indentation, per level. Do not use tabs, and do not put trailing whitespace.
17
For parentheses, three styles are accepted:
19
~~~python
20
# No indent.
21
thing = function(arg1, arg2)
22
# Hanging indent. Align to the contents, not to the bracket.
24
thing = function(arg1, arg2
25
arg3, arg4, arg5)
26
# Full indent. Here only one argument or variable or whatever is allowed per line.
28
# The closing bracket must be at the previous indent level.
29
# Any level is allowed, but it must be a multiple of 4.
30
thing = function(
31
arg1,
32
arg2,
33
arg3,
34
arg4
35
)
36
~~~
37
Collections should read like lists, not tables.
39
~~~python
40
fruits = ["apple", "tomato", "pear", "cherry", "plum", "melon", "grape", "aubergine",]
41
fruits = [
43
"apple",
44
"tomato",
45
"pear",
46
"cherry",
47
"plum",
48
"melon",
49
"grape",
50
"aubergine",
51
]
52
# Don't!
54
fruits = [
55
"apple", "tomato", "pear", "cherry",
56
"plum", "melon", "grape", "aubergine",
57
]
58
~~~
59
Additionally, for a collection meant to be expanded use a trailing comma.
61
For long expressions, begin the line with the operator and align the operand with the indentation level.
63
This is not permitted by PEP 8, but it follows mathematics and leads to nicer layouts.
64
~~~python
65
population = (population
66
+ births
67
+ immigrants
68
- deaths
69
- emigrants)
70
~~~
71
When the hanging indent could be mistaken for a block, add an empty line.
73
Backslashes are discouraged, but allowed if it is the only way to write your expression. For
75
example:
76
~~~python
78
really_long_variable_name_hopefully_yours_wont_be_as_long = \
79
"Really long value."
80
~~~
81
### Blank Line Rules
83
* Two between top-level class or function definitions.
84
* One between local functions or methods.
85
* One is allowed to separate related groups and logical sections.
86
* One at the end of the file.
87
* One below imports.
88
### Imports
90
Imports should be on separate lines. `from`-imports must import all objects on the same line though.
92
~~~python
93
import flask
94
import os
95
from models import User, Post
97
~~~
98
Imports should be ordered like this:
100
* `__future__` statements
101
* one blank line
102
* magic names (`__all__`, `__version__`)
103
* one blank line
104
* library imports
105
* library `from`-imports
106
* one blank line
107
* application imports
108
* application `from`-imports
109
Wildcard imports are discouraged and prohibited for libraries. However, they are fine if the module
111
defines `__all__`.
112
### Interior Whitespace
114
Never insert more than one space around operators and other symbols. Never add spaces just to align lines.
115
#### When to use
117
* around the lowest priority operators in an expression, comparisons, assignments, and logical operators, as well as the function annotation arrow
118
~~~python
119
# Do
120
thing += 10 + 2*thing
121
# Don't
122
thing+=10+2 * thing
123
# Acceptable; use your best judgement
124
thing += 10 + 2 * thing
125
~~~
126
* after the colon when defining a single-line clause, or an annotation
127
* after commas or semicolons
128
* after the comment sign `#`
129
#### When to avoid
130
* when passing keyword arguments or defining argument defaults, unless they are annotated
131
* inside any brackets
132
~~~python
133
# Do
134
function(arg1, arg2)
135
# Don't!
136
function( arg1, arg2 )
137
~~~
138
* after a trailing comma
139
~~~python
140
# Do
141
(0,)
142
# Don't!
143
(0, )
144
~~~
145
* before commas, semicolons or colons
146
~~~python
147
# Do
148
x, y = y, x
149
# Don't!
150
x , y = y , x
151
~~~
152
* around the slice operator `:`
153
* before an argument list
154
~~~python
155
# Do
156
function(arg1, arg2)
157
# Don't!
158
function (arg1, arg2)
159
~~~
160
* before the indexing operator
161
~~~python
162
# Do
163
dictionary["key"] = "Hello World!"
164
# Don't!
165
dictionary ["key"] = "Hello World!"
166
~~~
167
#### Other
169
Never use the semicolon for multiple statements; while allowed, it is discouraged as it hurts readability. Similarly discouraged are one-line clauses.
170
Strings
172
-------
173
Only use double quotes like `"` for strings: single quotes are harder to spot, and they conflict with the common apostrophe.
175
For docstrings you should follow [PEP 257](https://peps.python.org/pep-0257/). Additionally, docstrings should use Markdown to allow for a future tool to convert them to docs.
177
HOWEVER arguments should be described using the ReST syntax, as it is more readable in the code.
178
Other than this, they should be kept plaintext to prevent markup language battles (Python prefers
179
RST, but most use Markdown).
180
Naming
182
------
183
Identifiers must only use ASCII characters. Abbreviations should be kept to a minimum and it should be
185
made sure that they are widely used and accepted already.
186
(`id` for `identifier` or `repo` for `repository` is acceptable, but `avg` for `average` is not). Generally, names should be easy to pronounce.
187
Class names must use `UpperCamelCase` with the first letter of each word capitalised and no underscores.
189
Other names (function, variable) should use `snake_case` with all words lowercase and separated by underscores.
191
For instance and class methods, only name the first argument `self` or `cls`, respectively.
193
To avoid conflicts, append an underscore or use a synonym but do not corrupt the spelling (`class_` is better than `clss` or `klass` or `classs` or whatever).
195
Constants are an exception. They should use `UPPER_CASE` with underscores.
197
Non-public names should be prefixed with an underscore. In case it's really important to not use
199
them, use a double underscore to invoke name mangling.
200
Comments
202
--------
203
Block comments should be complete sentences; line comments don't need to. Write comments in
205
English and always use a space after the comment sign, as stated above, unless it's an UNIX
206
interpreter descriptor (`#!`) where you should not. Inside block comments, separate paragraphs
207
with an empty comment, like in Markdown. For a solo sentence, full stops are optional.
208
Avoid stating the obvious or contradicting the code.
209
Inline comments must be separated with more than one space from the statement, and they may be
211
aligned.
212
In comments, never alter the case of identifiers, as it may lead to confusion.
214
Leaving TODO comments as personal notes is allowed, but they should be removed before merging
216
or a release.
217
Programming
219
-----------
220
### OOP Guidelines
222
Do not use getters and setters for class attributes. If you do need to change some other things,
223
use properties.
224
Prefer overloading the operators; make using your objects as natural and Pythonic as possible.
226
### Exceptions
228
Make exceptions specific enough, so catching them can be explicit.
229
Do not use the bare `except` clause. Make `try` clauses as short as possible to avoid silencing
231
unrelated bugs.
232
### Other
234
Comparisons to singletons (`True`, `False`, `None` etc.) should be done with the identity operators
235
`is` and `is not`, not with the comparison operators. Use `is not`, not `not ... is`.
236
Unless it would be ambiguous, use the implicit truth test to check that numbers are different to
238
0, that containers have contents and similar tests.
239
Do not assign lambdas to identifiers. Make a real function instead.
241
Use `with` context managers to ensure resources are properly cleaned up.
243
Prefer making functions that take arguments and return a value instead of making them directly take
245
global variables or process the information such as writing.
246
Use the methods `startswith()` and `endswith()` instead of string slicing to check for prefixes
248
or suffixes.
249
To compare types, use `isinstance()` instead of the `is` operator with `type()` (this is one of
251
my problems with Python, but it's the standard).
252
Use a proper condition for `while` instead of a `while True` that `break`s.
254
Use `for` loops instead of `while` loops when possible, and use Pythonic iteration instead of
256
C-style iteration.
257
To call shells, use the `subprocess` module instead of `os.system()` and use the functions
259
that allow giving a *list* of arguments instead of a string, it leads to better security.
260
Similarly, avoid writing SQL manually, use Alchemy. If you must write SQL manually, be extra
262
careful.
263
Jinja style guide
265
-----------------
266
Jinja should be written like Python, with the following additions:
268
Tags should be written as `{% <content> %}` and expressions as `{{ <content> }}`. That is,
270
put spaces around the content.
271
Always indent tag contents, just like you would indent HTML tags! If a tag contains other tags
273
and it wouldn't disrupt whitespace, you should indent the contents.
274
The filter operator `|` should have spaces around it, unless it's in a more complex expression
276
when it shouldn't.
277
Translations should always be done with the `{% trans %}` tag provided by Babel, not with
279
`gettext()`, `_()` or others. No exceptions.
280
The quoting rules are as in Python, unless it's in an HTML attribute, in which case you should
282
use single quotes, as HTML takes precedence.
283
HTML style guide
285
----------------
286
HTML tags should be written in lowercase, with attributes in lowercase as well. Attribute values
288
should be quoted with double quotes. Attribute minimisation is suggested for boolean attributes.
289
Always indent tag contents with 4 spaces, except in plaintext tags like `pre` or `textarea`, where
291
you should not indent.
292
The tag should be multiple lines if the content is complex. Otherwise, mirror the page layout.
294
IDs or classes should be written in `kebab-case`. Names should be written in `snake_case` to
296
provide better compatibility with Python.
297
Also, when making custom tags, always use a hyphen in the tag name, to make sure they won't be
299
standardised in the future.
300
Event attributes are allowed as well, but please keep the JS inside shorter than 64 characters.
302
If you need more make a function in a script tag or a separate file.
303
CSS style guide
305
---------------
306
CSS selectors, properties and values should be written in lowercase. Custom properties should be
308
written in `kebab-case`.
309
Always indent the contents of a ruleset with 4 spaces.
311
Unlike some other style guides, we do not require each selector after a comma to be on a new line.
313
However, if they're too long, very complex or similar and they benefit from alignment, you should
314
do so.
315
IDs are preferred over classes when the element only appears once on the page.
317
Tag selectors are **allowed**! Style the default widgets as you see fit, because it leads to
319
cleaner HTML. We also apply a reset stylesheet to make sure the default styles are consistent.
320
In what scenario would you want an *unstyled* button in your site? Never! Then why always use
321
`<button class="btn btn-primary">` when it's the only kind of `<button>` your site has?
322
However, provide class-based alternatives for tag styles. For example, Efficient UI styles
324
`button` by default, but it also styles `.button` to allow hyperlinks or other elements to look
325
like buttons. Using both isn't needed though.
326
Also, selectors can be nested where it makes sense, however the `>` selector is preferred over
328
plain nesting, which is generally discouraged.
329
Use of fancy counters and data-attributes is allowed, but only for cosmetic purposes. We've got
331
server-side templating, profit from it!
332
JavaScript style guide
334
----------------------
335
JS should use double quotes for strings, and lowerCamelCase for names, and indenting should be 4 spaces.
337
Otherwise I can't comment, because JS is ugly by nature.
338