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Python Naming Convention

Python Naming Convention

  • UPPERCASE / UPPER_CASE_WITH_UNDERSCORES => module-level constants
  • lowercase / lower_case_with_underscores => for variable and function name.
  • CapitalizedWords (or CapWords, or CamelCase – so named because of the bumpy look of its letters [4]). This is also sometimes known as StudlyCaps. => CamelCase => Class
    • Note: When using acronyms in CapWords, capitalize all the letters of the acronym. Thus HTTPServerError is better than HttpServerError.
  • mixedCase (differs from CapitalizedWords by initial lowercase character!)
  • Capitalized_Words_With_Underscores (ugly!)
  • _single_leading_underscore: weak “internal use” indicator. E.g. from M import * does not import objects whose names start with an underscore.
  • single_trailing_underscore_: used by convention to avoid conflicts with Python keyword, e.g. tkinter.Toplevel(master, class_=’ClassName’)
  • __double_leading_underscore: when naming a class attribute, invokes name mangling (inside class FooBar, __boo becomes _FooBar__boo; see below).
  • __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.
  • Never use the characters ‘l’ (lowercase letter el), ‘O’ (uppercase letter oh), or ‘I’ (uppercase letter eye) as single character variable names.

Programming Recommendations

Use “is not” operator

  • Correct:
if foo is not None:
  • Wrong:
    if not foo is None:
    

Always use a def statement

  • Correct:
    def f(x): return 2*x
    
  • Wrong:
    f = lambda x: 2*x
    

all try/except clauses

  • Correct:
    try:
      value = collection[key]
    except KeyError:
      return key_not_found(key)
    else:
      return handle_value(value)
    
  • Wrong:
    try:
      # Too broad!
      return handle_value(collection[key])
    except KeyError:
      # Will also catch KeyError raised by handle_value()
      return key_not_found(key)
    

Context managers should be invoked through separate functions or methods

  • Correct:
with conn.begin_transaction():
    do_stuff_in_transaction(conn)
  • Wrong:
with conn:
    do_stuff_in_transaction(conn)

Be consistent in return statements

  • Correct:
def foo(x):
    if x >= 0:
        return math.sqrt(x)
    else:
        return None

def bar(x):
    if x < 0:
        return None
    return math.sqrt(x)
  • Wrong:
def foo(x):
    if x >= 0:
        return math.sqrt(x)

def bar(x):
    if x < 0:
        return
    return math.sqrt(x)

startswith, endswith

  • Use ‘‘.startswith() and ‘‘.endswith() instead of string slicing to check for prefixes or suffixes.
  • Correct: if foo.startswith(‘bar’):
  • Wrong: if foo[:3] == ‘bar’:

Object type comparisons

  • Correct: if isinstance(obj, int):
  • Wrong: if type(obj) is type(1):

Sequences, (strings, lists, tuples)

-For sequences, (strings, lists, tuples), use the fact that empty sequences are false:

  • Correct:
if not seq:
	if seq:
  • Wrong:
if len(seq):
	if not len(seq):

boolean value comparision

Don’t compare boolean values to True or False using ==:

  • Correct: if greeting:
  • Wrong: if greeting == True:
  • Worse: if greeting is True:

Assignment

If an assignment has a right hand side, then the equality sign should have exactly one space on both sides:

  • Correct: ```python code: int

class Point: coords: Tuple[int, int] label: str = ‘'

- Wrong:
```python
code:int  # No space after colon
code : int  # Space before colon

class Test:
    result: int=0  # No spaces around equality sign

References

  • https://peps.python.org/pep-0008/#programming-recommendations

Updated: