What is the naming convention in Python for variable and function? - python

Coming from a C# background the naming convention for variables and method names are usually either camelCase or PascalCase:
// C# example
string thisIsMyVariable = "a"
public void ThisIsMyMethod()
In Python, I have seen the above but I have also seen underscores being used:
# python example
this_is_my_variable = 'a'
def this_is_my_function():
Is there a more preferable, definitive coding style for Python?

See Python PEP 8: Function and Variable Names:
Function names should be lowercase, with words separated by underscores as necessary to improve readability.
Variable names follow the same convention as function names.
mixedCase is allowed only in contexts where that's already the prevailing style (e.g. threading.py), to retain backwards compatibility.

The Google Python Style Guide has the following convention:
module_name, package_name, ClassName, method_name, ExceptionName, function_name, GLOBAL_CONSTANT_NAME, global_var_name, instance_var_name, function_parameter_name, local_var_name.
A similar naming scheme should be applied to a CLASS_CONSTANT_NAME

David Goodger (in "Code Like a Pythonista" here) describes the PEP 8 recommendations as follows:
joined_lower for functions, methods,
attributes, variables
joined_lower or ALL_CAPS for
constants
StudlyCaps for classes
camelCase only to conform to
pre-existing conventions

As the Style Guide for Python Code admits,
The naming conventions of Python's
library are a bit of a mess, so we'll
never get this completely consistent
Note that this refers just to Python's standard library. If they can't get that consistent, then there hardly is much hope of having a generally-adhered-to convention for all Python code, is there?
From that, and the discussion here, I would deduce that it's not a horrible sin if one keeps using e.g. Java's or C#'s (clear and well-established) naming conventions for variables and functions when crossing over to Python. Keeping in mind, of course, that it is best to abide with whatever the prevailing style for a codebase / project / team happens to be. As the Python Style Guide points out, internal consistency matters most.
Feel free to dismiss me as a heretic. :-) Like the OP, I'm not a "Pythonista", not yet anyway.

As mentioned, PEP 8 says to use lower_case_with_underscores for variables, methods and functions.
I prefer using lower_case_with_underscores for variables and mixedCase for methods and functions makes the code more explicit and readable. Thus following the Zen of Python's "explicit is better than implicit" and "Readability counts"

There is PEP 8, as other answers show, but PEP 8 is only the styleguide for the standard library, and it's only taken as gospel therein. One of the most frequent deviations of PEP 8 for other pieces of code is the variable naming, specifically for methods. There is no single predominate style, although considering the volume of code that uses mixedCase, if one were to make a strict census one would probably end up with a version of PEP 8 with mixedCase. There is little other deviation from PEP 8 that is quite as common.

further to what #JohnTESlade has answered. Google's python style guide has some pretty neat recommendations,
Names to Avoid
single character names except for counters or iterators
dashes (-) in any package/module name
\__double_leading_and_trailing_underscore__ names (reserved by Python)
Naming Convention
"Internal" means internal to a module or protected or private within a class.
Prepending a single underscore (_) has some support for protecting module variables and functions (not included with import * from). Prepending a double underscore (__) to an instance variable or method effectively serves to make the variable or method private to its class (using name mangling).
Place related classes and top-level functions together in a module. Unlike Java, there is no need to limit yourself to one class per module.
Use CapWords for class names, but lower_with_under.py for module names. Although there are many existing modules named CapWords.py, this is now discouraged because it's confusing when the module happens to be named after a class. ("wait -- did I write import StringIO or from StringIO import StringIO?")
Guidelines derived from Guido's Recommendations

Most python people prefer underscores, but even I am using python since more than 5 years right now, I still do not like them. They just look ugly to me, but maybe that's all the Java in my head.
I simply like CamelCase better since it fits better with the way classes are named, It feels more logical to have SomeClass.doSomething() than SomeClass.do_something(). If you look around in the global module index in python, you will find both, which is due to the fact that it's a collection of libraries from various sources that grew overtime and not something that was developed by one company like Sun with strict coding rules. I would say the bottom line is: Use whatever you like better, it's just a question of personal taste.

Personally I try to use CamelCase for classes, mixedCase methods and functions. Variables are usually underscore separated (when I can remember). This way I can tell at a glance what exactly I'm calling, rather than everything looking the same.

There is a paper about this: http://www.cs.kent.edu/~jmaletic/papers/ICPC2010-CamelCaseUnderScoreClouds.pdf
TL;DR It says that snake_case is more readable than camelCase. That's why modern languages use (or should use) snake wherever they can.

The coding style is usually part of an organization's internal policy/convention standards, but I think in general, the all_lower_case_underscore_separator style (also called snake_case) is most common in python.

I personally use Java's naming conventions when developing in other programming languages as it is consistent and easy to follow. That way I am not continuously struggling over what conventions to use which shouldn't be the hardest part of my project!

Whether or not being in class or out of class:
A variable and function are lowercase as shown below:
name = "John"
def display(name):
print("John")
And if they're more than one word, they're separated with underscore "_" as shown below:
first_name = "John"
def display_first_name(first_name):
print(first_name)
And, if a variable is a constant, it's uppercase as shown below:
FIRST_NAME = "John"

Lenin has told... I'm from Java/C# world too. And SQL as well.
Scrutinized myself in attempts to find first sight understandable examples of complex constructions like list in the dictionary of lists where everything is an object.
As for me - camelCase or their variants should become standard for any language. Underscores should be preserved for complex sentences.

Typically, one follow the conventions used in the language's standard library.

Related

What is the capitalization standard for class names in the Python Standard Library?

The norm for Python standard library classes seems to be that class names are lowercase - this appears to hold true for built-ins such as str and int as well as for most classes that are part of standard library modules that must be imported such as datetime.date or datetime.datetime.
But, certain standard library classes such as enum.Enum and decimal.Decimal are capitalized. At first glance, it might seem that classes are capitalized when their name is equal to the module name, but that does not hold true in all cases (such as datetime.datetime).
What's the rationale/logic behind the capitalization conventions for class names in the Python Standard Library?
The Key Resources section of the Developers Guide lists PEP 8 as the style guide.
From PEP 8 Naming Conventions, emphasis mine.
The naming conventions of Python's library are a bit of a mess, so
we'll never get this completely consistent -- nevertheless, here are
the currently recommended naming standards. New modules and packages
(including third party frameworks) should be written to these
standards, but where an existing library has a different style,
internal consistency is preferred.
Also from PEP 8
A style guide is about consistency. Consistency with this style guide
is important. Consistency within a project is more important.
Consistency within one module or function is the most important.
...
Some other good reasons to ignore a particular guideline:
To be consistent with surrounding code that also breaks it (maybe for historic reasons) -- although this is also an opportunity to clean
up someone else's mess (in true XP style).
Because the code in question predates the introduction of the guideline and there is no other reason to be modifying that code.
You probably will never know why Standard Library naming conventions conflict with PEP 8 but it is probably a good idea to follow it for new stuff or even in your own projects.
Pep 8 is considered to be the standard style guide by many Python devs. This recommends to name classes using CamelCase/CapWords.
The naming convention for functions may be used instead in cases where the interface is documented and used primarily as a callable.
Note that there is a separate convention for builtin names: most builtin names are single words (or two words run together), with the CapWords convention used only for exception names and builtin constants.
Check this link for PEP8 naming conventions and standards.
datetime is a part of standard library,
Python’s standard library is very extensive, offering a wide range of facilities as indicated by the long table of contents listed below. The library contains built-in modules (written in C) that provide access to system functionality such as file I/O that would otherwise be inaccessible to Python programmers, as well as modules written in Python that provide standardized solutions for many problems that occur in everyday programming.
In some cases, like sklearn, nltk, django, the package names are all lowercase. This link will take you there.
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.
When an extension module written in C or C++ has an accompanying Python module that provides a higher level (e.g. more object oriented) interface, the C/C++ module has a leading underscore (e.g. _socket ).
I hope this covers all the questions.

Naming Variables and Functions

I'm using Python, but I think it's same for pretty much every programming languages. It has nothing to do with the functionalities, but I came to notice that when I see other people's codes, variable names with multiple words are connected, and the first letters of each words (except for the first one) are capitalized.
thisIsATypicalVariableNameWithMultipleWords = 0
But when using functions, usually nothing is capitalized and the words are connected by _.
this_is_a_typical_function_name_with_multiple_words()
Is this how the variables and functions are typically named? Thanks in advance.
You are looking at a naming convention, and such conventions are rather arbitrary but usually agreed upon in a style guide.
The Python developers have published such a style guide for Python: PEP 8 -- Style Guide for Python Code. It includes a section on naming conventions for Python code. You don't have to adhere to these, but it is a good idea to do so if you want to work with other Python developers where most do adhere to these conventions.
The style guide also provides you with names for the styles; your two specific styles (which are not the only two styles), are called mixedCase and lower_case_with_underscores.
mixedCase is no longer used in Python code; the style guide only mentions it as a legacy case for function names used by certain older standard library modules.
lower_case_with_underscores is the current recommended convention for function, method and attribute names.

Python double leading and trailing underscore usage for class attributes

In regards to naming conventions for class attributes, PEP 8 states:
__double_leading_and_trailing_underscore__: "magic" objects or attributes that live in user-controlled namespaces. E.g. __init__, __import__ or __file__. Never invent such names; only use them as documented.
Does this imply to never use this convention or only use in a "user-controlled namespace."
I have seen this used in other libraries not directly included within Python a few times. From what I gather, using this convention is more specific to implementing an API.
A couple of examples would be providing an __acl__ to a class in Pyramid, or adding __tablename__ to a class in SQLAlchemy.
Is using this convention in the context of an API OK, or should it only ever be used / reserved for Python?
Pyramid and SQLAlchemy have disobeyed the instruction not to invent such names.
It's not clear to me what you mean by "using this convention in the context of an API", but once they've invented the name, you don't have much choice but to use it as documented by them.
There's no difference between you inventing such names, and inventing them only in user-controlled namespaces. Since you're a user of Python, any namespace that you could put the name into is user-controlled. If you're modifying the Python source to add a new extension to the language that requires some "magic" name, then you can invent one. I expect if you're doing this, you'll usually be in communication with GvR one way or another, so you can ask his opinion directly :-)
What's happening here is that the library authors want a name that none of their users will use by accident to mean something else. The Python language also wants names that no user will use by accident to mean something else, so it "reserves" names of a particular format for use by the language. But then the library-writer has decided to "steal" one of those reserved names and use it anyway, because they feel that's the best way to avoid a clash with one of their users. They have tens of thousands of users, most of whom they don't know anything about. But there's only one Python language spec, and they have access to it. So if a clash occurs the library developers will know about it, which is the plus side, but it will be their fault and difficult to fix, which is the minus side.
Perhaps they're hoping that by using it, the have de facto reserved it for themselves, and that GvR will choose never to use a name that a popular library has already used. Or perhaps they've discussed it on the relevant mailing lists and obtained an exception to the usual rule -- I don't know whether there's a process for that.

Python Core Library and PEP8

I was trying to understand why Python is said to be a beautiful language. I was directed to the beauty of PEP 8... and it was strange. In fact it says that you can use any convention you want, just be consistent... and suddenly I found some strange things in the core library:
request()
getresponse()
set_debuglevel()
endheaders()
http://docs.python.org/py3k/library/http.client.html
The below functions are new in the Python 3.1. What part of PEP 8 convention is used here?
popitem()
move_to_end()
http://docs.python.org/py3k/library/collections.html
So my question is: is PEP 8 used in the core library, or not? Why is it like that?
Is there the same situation as in PHP where I cannot just remember the name of the function because there are possible all ways of writing the name?
Why PEP 8 is not used in the core library even for the new functions?
PEP 8 recommends using underscores as the default choice, but leaving them out is generally done for one of two reasons:
consistency with some other API (e.g. the current module, or a standard interface)
because leaving them out doesn't hurt readability (or even improves it)
To address the specific examples you cite:
popitem is a longstanding method on dict objects. Other APIs that adopt it retain that spelling (i.e. no underscore).
move_to_end is completely new. Despite other methods on the object omitting underscores, it follows the recommended PEP 8 convention of using underscores, since movetoend is hard to read (mainly because toe is a word, so most people's brains will have to back up and reparse once they notice the nd)
set_debuglevel (and the newer set_tunnel) should probably have left the underscore out for consistency with the rest of the HTTPConnection API. However, the original author may simply have preferred set_debuglevel tosetdebuglevel (note that debuglevel is also an argument to the HTTPConnection constructor, explaining the lack of a second underscore) and then the author of set_tunnel simply followed that example.
set_tunnel is actually another case where dropping the underscore arguably hurts readability. The juxtaposition of the two "t"s in settunnel isn't conducive to easy parsing.
Once these inconsistencies make it into a Python release module, it generally isn't worth the hassle to try and correct them (this was done to de-Javaify the threading module interface between Python 2 and Python 3, and the process was annoying enough that nobody else has volunteered to "fix" any other APIs afflicted by similar stylistic problems).
From PEP8:
But most importantly: know when to be
inconsistent -- sometimes the style
guide just doesn't apply. When in doubt, use your best judgment. Look
at other examples and decide what looks best. And don't hesitate to
ask!
What you have mentioned here is somewhat consistent with the PEP8 guidelines; actually, the main inconsistencies are in other parts, usually with CamelCase.
The Python standard library is not as tightly controlled as it could be, and the style of modules varies. I'm not sure what your examples are meant to illustrate, but it is true that Python's library does not have one voice, as Java's does, or Win32. The language (and library) are built by an all-volunteer crew, with no corporation paying salaries to people dedicated to the language, and it sometimes shows.
Of course, I believe other factors outweigh this negative, but it is a negative nonetheless.

Python Notation?

I've just started using Python and I was thinking about which notation I should use. I've read the PEP 8 guide about notation for Python and I agree with most stuff there except function names (which I prefer in mixedCase style).
In C++ I use a modified version of the Hungarian notation where I don't include information about type but only about the scope of a variable (for instance lVariable for a local variable and mVariable for a member variable of a class, g for global, s for static, in for a function's input and out for a function's output.)
I don't know if this notation style has a name but I was wondering whether it's a good idea not to use such a notation style in Python. I am not extremely familiar with Python so you guys/gals might see issues that I can't imagine yet.
I'm also interested to see what you think of it in general :) Some people might say it makes the code less readable, but I've become used to it and code written without these labels is the code that is less readable for me.
(Almost every Python programmer will say it makes the code less readable, but I've become used to it and code written without these labels is the code that is less readable for me)
FTFY.
Seriously though, it will help you but confuse and annoy other Python programmers that try to read your code.
This also isn't as necessary because of how Python itself works. For example you would never need your "mVariable" form because it's obvious in Python:
class Example(object):
def__init__(self):
self.my_member_var = "Hello"
def sample(self):
print self.my_member_var
e = Example()
e.sample()
print e.my_member_var
No matter how you access a member variable (using self.foo or myinstance.foo) it's always clear that it's a member.
The other cases might not be so painfully obvious, but if your code isn't simple enough that a reader can keep in mind "the 'names' variable is a parameter" while reading a function you're probably doing something wrong.
Use PEP-8. It is almost universal in the Python world.
I violate PEP8 in my code. I use:
lowercaseCamelCase for methods and functions
_prefixedWithUnderscoreLowercaseCamelCase for "private" methods
underscore_spaced for variables (any)
_prefixed_with_underscore_variables for "private" self variables (attributes)
CapitalizedCamelCase for classes and modules (although I am moving to lowercasedmodules)
I never liked hungarian notation. A variable name should be easy and concise, provide sufficient information to be clear where (in which scope) it's used and what is its purpose, easy to read, concerned about the meaning of what it refers to, not its technical mumbo-jumbo (eg. type).
The reason behind my violations are due to practical considerations, and previous experience.
in C++ and Java, it's tradition to have CapitalizedCamel for classes and lowercaseCamel for member functions.
I worked on a codebase where the underscore prefix was used to indicate private but not that much private. We did not want to mess with the python name mangling (double underscore). This gave us the chance to violate a bit the formalities and peek the internal class state during unit testing.
There exists a handy pep-8 compliance script you can run against your code:
http://github.com/cburroughs/pep8.py/tree/master
It'll depend on the project and the target audience.
If you're building an open source application/plug-in/library, stick with the PEP guidelines.
If this is a project for your company, stick with the company conventions, or something similar.
If this is your own personal project, then use what ever convention is fluid and easy for you to use.
I hope this makes sense.
You should simply be consistent with your naming conventions in your own code. However, if you intend to release your code to other developers you should stick to PEP-8.
For example the 4 spaces vs. 1 tab is a big deal when you have a collaborative project. People submitting code to a source repository with tabs requires developers to be constantly arguing over whitespace issues (which in Python is a BIG deal).
Python and all languages have preferred conventions. You should learn them.
Java likes mixedCaseStuff.
C likes szHungarianNotation.
Python prefers stuff_with_underscores.
You can write Java code with_python_type_function_names.
You can write Python code with javaStyleMixedCaseFunctionNamesThatAreSupposedToBeReallyExplict
as long as your consistant :p

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