Basically when I have a python file like:
python-code.py
and use:
import (python-code)
the interpreter gives me syntax error.
Any ideas on how to fix it? Are dashes illegal in python file names?
You should check out PEP 8, the Style Guide for Python Code:
Package and Module Names Modules should have short, all-lowercase names. Underscores can be used in the module name if it improves readability. Python packages should also have short, all-lowercase names, although the use of underscores is discouraged.
Since module names are mapped to file names, and some file systems are case insensitive and truncate long names, it is important that module names be chosen to be fairly short -- this won't be a problem on Unix, but it may be a problem when the code is transported to older Mac or Windows versions, or DOS.
In other words: rename your file :)
One other thing to note in your code is that import is not a function. So import(python-code) should be import python-code which, as some have already mentioned, is interpreted as "import python minus code", not what you intended. If you really need to import a file with a dash in its name, you can do the following::
python_code = __import__('python-code')
But, as also mentioned above, this is not really recommended. You should change the filename if it's something you control.
TLDR
Dashes are not illegal but you should not use them for 3 reasons:
You need special syntax to import files with dashes
Nobody expects a module name with a dash
It's against the recommendations of the Python Style Guide
If you definitely need to import a file name with a dash the special syntax is this:
module_name = __import__('module-name')
Curious about why we need special syntax?
The reason for the special syntax is that when you write import somename you're creating a module object with identifier somename (so you can later use it with e.g. somename.funcname). Of course module-name is not a valid identifier and hence the special syntax that gives a valid one.
You don't get why module-name is not valid identifier?
Don't worry -- I didn't either. Here's a tip to help you: Look at this python line: x=var1-var2. Do you see a subtraction on the right side of the assignment or a variable name with a dash?
PS
Nothing original in my answer except including what I considered to be the most relevant bits of information from all other answers in one place
The problem is that python-code is not an identifier. The parser sees this as python minus code. Of course this won't do what you're asking. You will need to use a filename that is also a valid python identifier. Try replacing the - with an underscore.
On Python 3 use import_module:
from importlib import import_module
python_code = import_module('python-code')
More generally,
import_module('package.subpackage.module')
You could probably import it through some __import__ hack, but if you don't already know how, you shouldn't. Python module names should be valid variable names ("identifiers") -- that means if you have a module foo_bar, you can use it from within Python (print foo_bar). You wouldn't be able to do so with a weird name (print foo-bar -> syntax error).
Although proper file naming is the best course, if python-code is not under our control, a hack using __import__ is better than copying, renaming, or otherwise messing around with other authors' code. However, I tried and it didn't work unless I renamed the file adding the .py extension. After looking at the doc to derive how to get a description for .py, I ended up with this:
import imp
try:
python_code_file = open("python-code")
python_code = imp.load_module('python_code', python_code_file, './python-code', ('.py', 'U', 1))
finally:
python_code_file.close()
It created a new file python-codec on the first run.
Related
I used PyScaffold to create a template for a PyPi package I am creating, bbox-utils. The generated __init__.py is as follows:
from pkg_resources import DistributionNotFound, get_distribution
try:
# Change here if project is renamed and does not equal the package name
dist_name = "bbox-utils"
__version__ = get_distribution(dist_name).version
except DistributionNotFound: # pragma: no cover
__version__ = "unknown"
finally:
del get_distribution, DistributionNotFound
I'm a bit confused what name to use for dist_name. I tried doing:
>>> from pkg_resources import DistributionNotFound, get_distribution
>>> get_distribution('bbox_utils').version
'0.0.1'
>>> get_distribution('bbox-utils').version
'0.0.1'
and I get the same version whether I replace the hyphen with an underscore or leave it as is. Which should I do?
Edit:
Here is the GitHub repo
Here is PyPi link
You generally should not name your packages or modules using dashes although you can. Since the import statement does not use quotes, using a dash is interpreted as using a minus sign, which will result in an illegal syntax during import if using the dash name.
There are ways around this, such as importing with underscores but installing via pip/searching pypi with dashes, but it is a needless inconsistency that can cause frustration. Generally the python approach is to be able to import modules as valid module objects whose variable name equals the actual module name. When naming projects, it is therefore better to use underscores instead of dashes.
That being said, pkg_resources seems to actually replace all non-alphanumeric and non-dot characters with dashes when resolving project names.
assert(get_distribution('bbox_utils').project_name == 'bbox-utils')
assert(get_distribution('bbox-utils').project_name == 'bbox-utils')
So you should be able to use either expression interchangeably in the code snippet in the question.
I've got a set of file directories that I am manipulating with python. However, all I care about is the last two levels of the directory. So if I had
"topdirectory/sub1/subsub1/subsubsub1/target"
"topdirectory/sub1/target"
The necesary returned strings would be
"subsubsub1/target"
and
"sub1/target"
I know python has a split string type method, but how can I tell it to only grab the LAST 2 components separated by delimeters?
Edit : Sorry guys, I should have explained that this is not REALLY a directory/file setup, but a timeseries DB that very closely resembles one. I figured it would just be easier to explain that way. The paths are essentially directories/files, but since it is a database, using the OS utilites wouldn't have any effect.
The os.path module contains a split function for this. It returns the dirname and the basename. Run it twice and you have the last two bases.
Obviously, you want some checking that there are two or more bases as well.
Try
"topdirectory/sub1/subsub1/subsubsub1/target".rsplit('/',2)[-2:]
This approach works for any string in general.
But as stated in the comments, if you refer to the system path, I'd rather use os module as suggested by Sean Perry. Note that on different operating system, delimiter can be different, etc.
What is the idomatic/canoncial/best way to get a sibling file (name) in Python 2.7?
That is, if there is file like 'C:\\path\\file.bin' or '/path/file.bin',
how to get 'C:\\path\\anothername.anotherext' or '/path/anothername.anotherext'.
String manipulation, searching for last path separator and replacing the part after that, would of course work, but this seems awfully crude.
In other words, what is idiomatic Python equivalent(s) of these Java snippets:
File sibling = new File(file.getParent(), siblingName);
Or a bit longer for pathname strings:
String siblingPathName = new File(new File(filePathName).getParent(), siblingName).toString();
Note: Java being used above is not relevant to the question.
Note2: If Python 3 has a new way, it would be nice to know that too, even though I'm using Python 2.7 atm.
Use os.path.dirname to get the directory of the file, and then os.path.join to add the sibling's name.
os.path.join(os.path.dirname(f), siblingname)
So i was thinking that in order to implement such a feature in a console application , where appending a question mark at the end of a function name will pour out it's doc string , i would have probably used a feature like metaclasses , where upon definition/import , i'd duplicate all the module member names and produce new ones just for typing out doc strings.
Then i noticed that you don't need actual parenthesis to call the helper functions and python doesn't actually allow you to put a question mark at the end of the function name anyway.... So is this done in python or am i just wasting my time trying to figure this out?
Thanks in advance
It's not done the way you're imagining. ipython reads your command prompt input as a line of text, so it has a chance to check if it ends with a question mark before it passes it on to eval (or whatever). If it does, it runs help(name) instead of what you typed.
AST looks a little heavy-duty, but you can get a feel for how this works by checking out the module code. It gives you a lightweight interpreter that you can extend with syntax of this sort if you want.
Have a look at the IPython.core.inputsplitter module for the code that parses the raw input line for things like ?, !, /, %, etc.
ipython uses AST, you can customize the syntax parsing and create a new ipython fork.
may help
I'm pretty new to Python, and I want to develop my first serious open source project. I want to ask what is the common coding style for python projects. I'll put also what I'm doing right now.
1.- What is the most widely used column width? (the eternal question)
I'm currently sticking to 80 columns (and it's a pain!)
2.- What quotes to use? (I've seen everything and PEP 8 does not mention anything clear)
I'm using single quotes for everything but docstrings, which use triple double quotes.
3.- Where do I put my imports?
I'm putting them at file header in this order.
import sys
import -rest of python modules needed-
import whatever
import -rest of application modules-
<code here>
4.- Can I use "import whatever.function as blah"?
I saw some documents that disregard doing this.
5.- Tabs or spaces for indenting?
Currently using 4 spaces tabs.
6.- Variable naming style?
I'm using lowercase for everything but classes, which I put in camelCase.
Anything you would recommend?
PEP 8 is pretty much "the root" of all common style guides.
Google's Python style guide has some parts that are quite well thought of, but others are idiosyncratic (the two-space indents instead of the popular four-space ones, and the CamelCase style for functions and methods instead of the camel_case style, are pretty major idiosyncrasies).
On to your specific questions:
1.- What is the most widely used column width? (the eternal question)
I'm currently sticking to 80 columns
(and it's a pain!)
80 columns is most popular
2.- What quotes to use? (I've seen everything and PEP 8 does not mention
anything clear) I'm using single
quotes for everything but docstrings,
which use triple double quotes.
I prefer the style you're using, but even Google was not able to reach a consensus about this:-(
3.- Where do I put my imports? I'm putting them at file header in this
order.
import sys import -rest of python
modules needed-
import whatever import -rest of
application modules-
Yes, excellent choice, and popular too.
4.- Can I use "import whatever.function as blah"? I saw some
documents that disregard doing this.
I strongly recommend you always import modules -- not specific names from inside a module. This is not just style -- there are strong advantages e.g. in testability in doing that. The as clause is fine, to shorten a module's name or avoid clashes.
5.- Tabs or spaces for indenting? Currently using 4 spaces tabs.
Overwhelmingly most popular.
6.- Variable naming style? I'm using lowercase for everything but classes,
which I put in camelCase.
Almost everybody names classes with uppercase initial and constants with all-uppercase.
1.- Most everyone has a 16:9 or 16:10 monitor now days. Even if they don't have a wide-screen they have lots of pixels, 80 cols isn't a big practical deal breaker like it was when everyone was hacking at the command line in a remote terminal window on a 4:3 monitor at 320 X 240. I usually end the line when it gets too long, which is subjective. I am at 2048 X 1152 on a 23" Monitor X 2.
2.- Single quotes by default so you don't have to escape Double quotes, Double quotes when you need to embed single quotes, and Triple quotes for strings with embedded newlines.
3.- Put them at the top of the file, sometimes you put them in the main function if they aren't needed globally to the module.
4.- It is a common idiom to rename some modules. A good example is the following.
try:
# for Python 2.6.x
import json
except ImportError:
# for previous Pythons
try:
import simplejson as json
except ImportError:
sys.exit('easy_install simplejson')
but the preferred way to import just a class or function is from module import xxx with the optional as yyy if needed
5.- Always use SPACES! 2 or 4 as long as no TABS
6.- Classes should up UpperCaseCamelStyle, variables are lowercase sometimes lowerCamelCase or sometimes all_lowecase_separated_by_underscores, as are function names. "Constants" should be ALL_UPPER_CASE_SEPARATED_BY_UNDERSCORES
When in doubt refer to the PEP 8, the Python source, existing conventions in a code base. But the most import thing is to be internally consistent as possible. All Python code should look like it was written by the same person when ever possible.
Since I'm really crazy about "styling" I'll write down the guidelines that I currently use in a near 8k SLOC project with about 35 files, most of it matches PEP8.
PEP8 says 79(WTF?), I go with 80 and I'm used to it now. Less eye movement after all!
Docstrings and stuff that spans multiple lines in '''. Everything else in ''. Also I don't like double quotes, I only use single quotes all the time... guess that's because I came form the JavaScript corner, where it's just easier too use '', because that way you don't have to escape all the HTML stuff :O
At the head, built-in before custom application code. But I also go with a "fail early" approach, so if there's something that's version depended(GTK for example) I'd import that first.
Depends, most of the times I go with import foo and from foo import, but there a certain cases(e.G. the name is already defined by another import) were I use from foo import bar as bla too.
4 Spaces. Period. If you really want to use tabs, make sure to convert them to spaces before committing when working with SCM. BUT NEVER(!) MIX TABS AND SPACES!!! It can AND WILL introduce horrible bugs.
some_method or foo_function, a CONSTANT, MyClass.
Also you can argue about indentation in cases where a method call or something spans multiple lines, and you can argue about which line continuation style you will use. Either surround everything with () or do the \ at the end of the line thingy. I do the latter, and I also place operators and other stuff at the start of the next line.
# always insert a newline after a wrapped one
from bla import foo, test, goo, \
another_thing
def some_method_thats_too_long_for_80_columns(foo_argument, bar_argument, bla_argument,
baz_argument):
do_something(test, bla, baz)
value = 123 * foo + ten \
- bla
if test > 20 \
and x < 4:
test_something()
elif foo > 7 \
and bla == 2 \
or me == blaaaaaa:
test_the_megamoth()
Also I have some guidelines for comparison operations, I always use is(not) to check against None True False and I never do an implicit boolean comparison like if foo:, I always do if foo is True:, dynamic typing is nice but in some cases I just want to be sure that the thing does the right thing!
Another thing that I do is to never use empty strings! They are in a constants file, in the rest of the code I have stuff like username == UNSET_USERNAME or label = UNSET_LABEL it's just more descriptive that way!
I also have some strict whitespace guidelines and other crazy stuff, but I like it(because I'm crazy about it), I even wrote a script which checks my code:
http://github.com/BonsaiDen/Atarashii/blob/master/checkstyle
WARNING(!): It will hurt your feelings! Even more than JSLint does...
But that's just my 2 cents.