too-many-branches (PLR0912)
Derived from the Pylint linter.
What it does
Checks for functions or methods with too many branches, including (nested)
if, elif, and else branches, for loops, try-except clauses, and
match and case statements.
By default, this rule allows up to 12 branches. This can be configured
using the lint.pylint.max-branches option.
Why is this bad?
Functions or methods with many branches are harder to understand and maintain than functions or methods with fewer branches.
Example
Given:
def capital(country):
if country == "Australia":
return "Canberra"
elif country == "Brazil":
return "Brasilia"
elif country == "Canada":
return "Ottawa"
elif country == "England":
return "London"
elif country == "France":
return "Paris"
elif country == "Germany":
return "Berlin"
elif country == "Poland":
return "Warsaw"
elif country == "Romania":
return "Bucharest"
elif country == "Spain":
return "Madrid"
elif country == "Thailand":
return "Bangkok"
elif country == "Turkey":
return "Ankara"
elif country == "United States":
return "Washington"
else:
return "Unknown" # 13th branch
Use instead:
def capital(country):
capitals = {
"Australia": "Canberra",
"Brazil": "Brasilia",
"Canada": "Ottawa",
"England": "London",
"France": "Paris",
"Germany": "Berlin",
"Poland": "Warsaw",
"Romania": "Bucharest",
"Spain": "Madrid",
"Thailand": "Bangkok",
"Turkey": "Ankara",
"United States": "Washington",
}
city = capitals.get(country, "Unknown")
return city
Given:
def grades_to_average_number(grades):
numbers = []
for grade in grades: # 1st branch
if len(grade) not in {1, 2}:
raise ValueError(f"Invalid grade: {grade}")
if len(grade) == 2 and grade[1] not in {"+", "-"}:
raise ValueError(f"Invalid grade: {grade}")
letter = grade[0]
if letter in {"F", "E"}:
number = 0.0
elif letter == "D":
number = 1.0
elif letter == "C":
number = 2.0
elif letter == "B":
number = 3.0
elif letter == "A":
number = 4.0
else:
raise ValueError(f"Invalid grade: {grade}")
modifier = 0.0
if letter != "F" and grade[-1] == "+":
modifier = 0.3
elif letter != "F" and grade[-1] == "-":
modifier = -0.3
numbers.append(max(0.0, min(number + modifier, 4.0)))
try:
return sum(numbers) / len(numbers)
except ZeroDivisionError: # 13th branch
return 0
Use instead:
def grades_to_average_number(grades):
grade_values = {"F": 0.0, "E": 0.0, "D": 1.0, "C": 2.0, "B": 3.0, "A": 4.0}
modifier_values = {"+": 0.3, "-": -0.3}
numbers = []
for grade in grades:
if len(grade) not in {1, 2}:
raise ValueError(f"Invalid grade: {grade}")
letter = grade[0]
if letter not in grade_values:
raise ValueError(f"Invalid grade: {grade}")
number = grade_values[letter]
if len(grade) == 2 and grade[1] not in modifier_values:
raise ValueError(f"Invalid grade: {grade}")
modifier = modifier_values.get(grade[-1], 0.0)
if letter == "F":
numbers.append(0.0)
else:
numbers.append(max(0.0, min(number + modifier, 4.0)))
try:
return sum(numbers) / len(numbers)
except ZeroDivisionError:
return 0