Python Naming Convention

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• 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.
• singletrailing_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 _FooBarboo; 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

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Use “is not” operator

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• Correct:

if foo is not None:

• Wrong:

if not foo is None:

Always use a def statement

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• Correct:

def f(x): return 2*x

• Wrong:

f = lambda x: 2*x

all try/except clauses

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• 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

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• Correct:

with conn.begin_transaction():
    do_stuff_in_transaction(conn)

• Wrong:

with conn:
    do_stuff_in_transaction(conn)

Be consistent in return statements

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• 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

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• 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

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

Sequences, (strings, lists, tuples)

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-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

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

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

Assignment

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

• Correct:

code: int

class Point:
    coords: Tuple[int, int]
    label: str = '<unknown>'

• Wrong:

code:int  # No space after colon
code : int  # Space before colon

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

References

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