So here is an example of a multiline string in vscode/python:
Cursor is after the p , and then you press enter, and end up like this:
i.e. the string ends up indented, which seems what you almost never want - why have an arbitratly amount of whitespace on the next line of this string ?
Is there any way change this in vscode, i.e. for multiline strings, it should end up with this:
I think this problem is related to different coding styles of different people.
For example,
def example(x):
if x:
a = '''
This is help
'''
def example(x):
if x:
a = '''This is help
'''
The automatic indenting of vscode line breaks is based on code blocks. If you want Vscode can identify multiline string, I think it would be better to submit future request in github. I've submitted this issue for you.
I am not 100% sure if what OP meant is just to refer to the indentation in the editor (namely, VSC) or if, by this:
i.e. the string ends up indented, which seems what you almost never want - why have an arbitrary amount of white space on the next line of this string?
...they also meant to refer to the actual output of the multi-line string,
(or also, just in case anybody else finds this post looking for a way to avoid this affecting the actual output of the multi-line string), I'd like to add as a complementary answer (cannot comment yet) that this was already beautifully answered here.
If that's the case and you're reading this for that reason, in short, all you want is to import the standard lib 'inspect' and post-process your string with it, using the cleandoc method.
Without breaking the indentation in your IDE, this method makes sure to give you the string output you actually expected:
All leading whitespace is removed from the first line. Any leading whitespace that can be uniformly removed from the second line onwards is removed. Empty lines at the beginning and end are subsequently removed. Also, all tabs are expanded to spaces.
(From the docs link above)
Hope that helps anyone.
Related
My CS teacher told me that """ triple quotations are used as comments, yet I learned it as strings with line-breaks and indentations. This got me thinking about - does python completely triple quote lines outside of relevant statements?
"""is this completely ignored like a comment"""
-or, is the computer actually considering this?
Triple quoted strings are used as comment by many developers but it is actually not a comment, it is similar to regular strings in python but it allows the string to be in multi-line. You will find no official reference for triple quoted strings to be a comment.
In python, there is only one type of comment that starts with hash # and can contain only a single line of text.
According to PEP 257, it can however be used as a docstring, which is again not really a comment.
def foo():
"""
Developer friendly text for describing the purpose of function
Some test cases used by different unit testing libraries
"""
<body of the function>
You can just assign them to a variable as you do with single quoted strings:
x = """a multi-line text
enclosed by
triple quotes
"""
Furthermore, if you try in repl, triple quoted strings get printed, had it really been a comment, should it have been printed?:
>>> #comment
>>> """triple quoted"""
'triple quoted'
As someone else already pointed out, they are indeed strings and not comments in Python. I just wanted to add a little more context about your question of "is the computer actually considering it?"
The answer is yes, since it isn't a comment. Take the below code for example:
def my_func():
"""
Some string
"""
print("Hello World!")
my_func()
Trying to run this will actually produce a syntax error because of the indentation.
So as far as I know, triple quotes can be used for both purposes but # is the standard for commenting.
According to this website, what I can understand is that ''' This '''
can be used as a comment and because they are handled as docstrings technically (not tested) ' This ' can also act as a comment depending on where put it. However, even though single and triple quotes can be used as comments, it does not mean that they are comments. For example, # comments are compeletely ignored by the interpreter whereas ''' comments might be loaded into memory (just a probable guess, not confirmed). But from what I can tell, they aren't handled as comments as shown below:
So they are not but they can be used as comments. Generally speaking, use #.
EDIT:
As #BTables pointed out, you will get an indentation error if you don't indent them correctly. So they are indeed handled as strings.
I am writing a lexer + parser in JFlex + CUP, and I wanted to have Python-like syntax regarding blocks; that is, indentation marks the block level.
I am unsure of how to tackle this, and whether it should be done at the lexical or sintax level.
My current approach is to solve the issue at the lexical level - newlines are parsed as instruction separators, and when one is processed I move the lexer to a special state which checks how many characters are in front of the new line and remembers in which column the last line started, and accordingly introduces and open block or close block character.
However, I am running into all sort of trouble. For example:
JFlex cannot match empty strings, so my instructions need to have at least one blanck after every newline.
I cannot close two blocks at the same time with this approach.
Is my approach correct? Should I be doing things different?
Your approach of handling indents in the lexer rather than the parser is correct. Well, it’s doable either way, but this is usually the easier way, and it’s the way Python itself (or at least CPython and PyPy) does it.
I don’t know much about JFlex, and you haven’t given us any code to work with, but I can explain in general terms.
For your first problem, you're already putting the lexer into a special state after the newline, so that "grab 0 or more spaces" should be doable by escaping from the normal flow of things and just running a regex against the line.
For your second problem, the simplest solution (and the one Python uses) is to keep a stack of indents. I'll demonstrate something a bit simpler than what Python does.
First:
indents = [0]
After each newline, grab a run of 0 or more spaces as spaces. Then:
if len(spaces) == indents[-1]:
pass
elif len(spaces) > indents[-1]:
indents.append(len(spaces))
emit(INDENT_TOKEN)
else:
while len(spaces) != indents[-1]:
indents.pop()
emit(DEDENT_TOKEN)
Now your parser just sees INDENT_TOKEN and DEDENT_TOKEN, which are no different from, say, OPEN_BRACE_TOKEN and CLOSE_BRACE_TOKEN in a C-like language.
Of you’d want better error handling—raise some kind of tokenizer error rather than an implicit IndexError, maybe use < instead of != so you can detect that you’ve gone too far instead of exhausting the stack (for better error recovery if you want to continue to emit further errors instead of bailing at the first one), etc.
For real-life example code (with error handling, and tabs as well as spaces, and backslash newline escaping, and handling non-syntactic indentation inside of parenthesized expressions, etc.), see the tokenize docs and source in the stdlib.
I recently encountered the common "unexpected indent" problem when trying to evaluate python code by copying them from PyDev and Emacs into a python interpreter.
After trying to fix tab/spaces and some searches, I found the cause in this answer:
This error can also occur when pasting something into the Python
interpreter (terminal/console).
Note that the interpreter interprets an empty line as the end of an
expression, so if you paste in something like
def my_function():
x = 3
y = 7
the interpreter will interpret the empty line before y = 7 as the end
of the expression ...
, which is exactly the case in my situation. And there is also a comment to the answer which points out a solution:
key being that blank lines within the function definition are fine,
but they still must have the initial whitespace since Python
interprets any blank line as the end of the function
But the solution is impractical as I have many empty lines that are problematic for the interpreter. My question is:
Is there a method/tool to automatically insert the right number of initial whitespaces to empty lines so that I can copy-and-paste my code from an editor to an interpreter?
Don't bother with inserting spaces. Tell the interpreter to execute a block of text instead:
>>> exec(r'''
<paste your code>
''')
The r''' ... ''' tripple-quoted string preserves escapes and newlines. Sometimes (though in my experience, rarely) you need to use r""" ... """ instead, when the code block contains tripple-quoted strings using single quotes.
Another option is to switch to using IPython to do your day-to-day testing of pasted code, which handles pasted code with blank lines natively.
This question already has answers here:
Python comments: # vs. strings
(3 answers)
Closed 9 years ago.
I know two ways of leaving comments in python. One is using """ and the other is using #. I know that the first can be used to return a functions help as a benefit. But when should I use one and when the other? And also how do I have to leave comments? Do I have to press tab and arrange the first line of comment with the the command beneath it? Or do I have to start from the beginning of the line?
No, there is only one way of commenting, using #:
A comment starts with a hash character (#) that is not part of a string literal, and ends at the end of the physical line.
Triple quoting, """, creates a string object, which happens to be used as the docstring when it is the first line of a function, module or a a class. Triple quoting is useful in many other places too, but should not be confused with commenting. You can use a triple quoted string like any other string literal, with the specific benefit that you can use actual newlines in your source code instead of having to use \n escape characters.
Although it can be used to disable a block of code by turning it into a multi-line string instead, you really should not do this. Use proper source code control and simply delete the block, or use an editor that lets you comment out whole blocks by inserting # for you instead.
For actual comments, use #. The Python style guide (PEP 8) has some things to say about when and how to use commenting; it has this to say about indentation:
Block comments generally apply to some (or all) code that follows them, and are indented to the same level as that code. Each line of a block comment starts with a # and a single space (unless it is indented text inside the comment).
I have an invisible expected an indented block error, which is likely caused by me using tabs instead of spaces.
When I open the "find/replace" window and try to enter TAB in the find field IDLE unsurprisingly just skips to the replace field.
How do I do this?
Final update:
Thank you for all answers, much appreciated. My problem was that python wants the function comments to be indented too, that is
def imdheladumb():
"""
I'm dum as hel
"""
does not work, it needs to be
def imdheladumb():
"""
I'm dum as hel
"""
IDLE doesn't let you search to literal tab characters. You can paste one into the search box (as suggested by will), but it will never match anything.
However, it does let you do regular expression searches, and the regular expression \t will match a literal tab. So, turn on the Regular expression checkbox, and put '\t in the Find: box, and 4 or 8 spaces (as appropriate) in the Replace: box.
But, as will suggested, it's better to use IDLE's features instead of trying to do things manually: Select the block of code with tabbed (or inconsistent) indentation, go to the Format menu, and select Untabify Region. (Or just hit control-6.) If the tabs were inserted with an editor that uses 4-space tabs, you may need to first use New Indent Width and change it to 4, then Untabify Region.
IDLE doesn't have any code to guess what your tab size was when you wrote the inconsistent code. The only editor I know of that does is emacs. If you just open the file in emacs, it will try to guess your settings, and then you can select the whole buffer and untabify-region. If it guessed right, you're golden; if it guessed wrong, don't save the buffer, because now it'll be even harder to fix. (If you're one of the 3 people in the world who knows how to read emacs lisp but doesn't like emacs, you could look through the python-mode.el source and see how it does its magic.)
A generic way to do this is to just copy a tab character from the document (or just do one in any random text editor and copy it) and then put that into the field.
You could try putting \t in there, but that only works in some editors.
Most IDEs have a function to automatically replace tabs with a predefined number of spaces. I suggest turning that on...
EDIT: doing a standard find and replace could be dangerous if you're using tabs somewhere else for any reason.
If you look here, there's an option called "tabify region". That might be more interesting for you.
There should be an app for that. ;)
If you enjoy overkill, what about running your code through a regular expression like:
re.sub('\t', '\s\s\s\s', yourCode)
For those people having the problem, the new version of VSCode can solve this easily.
Click on Tab Sizes at the bottom of the page.
Select Convert Indentation to Spaces from the "Select Action" menu that pops up.