高级用法 Advance

递归 Recursion

# 3! = 3 * 2 * 1 = 6

def factorial(n):
    if n== 1: return 1
    reutrn n * factorial(n-1)
factorial(3) # 6

装饰器 Decorators

def logtime(func):
    def wrapper():
        # do something before
        print("before")
        val = func()
        print("after")
        # do something after
        return val
    return wrapper

@logtime
def hello():
    print("hello")

hello()
# before
# hello
# after

Docstrings

def increment(n):
    """Increment a number"""
    return n + 1

"""Dog module

This module does ... blablabla and provides the following classes:

- Dog
...
"""

class Dog(Animal):
    """A class representing a dog"""
    def __init__(self, name, age):
        """Initialize a new dog"""
        self.name = name
        self.age = age

    def bark(self):
        """Let the dog bark"""
        print("woof!")

print(help(Dog))

Annotations

def increment(n: int) -> int:
    return n + 1

count: int = 0

Eceptions

try:
    # some lines of code
except <ERROR1>:
    # handler <ERROR1>
except <ERROR2>:
    # handler <ERROR2>
except:
    # handler except
else:
    # no exceptions were raised, the code ran successfully
finally:
    # do something in any case

try:
    result = 2 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")
finally:
    result = 1
print(result)
# Cannot divide by zero!
# 1

try:
    raise Exception("An error!")
except Exception as error:
    print("inside")
    print(error)

# An error!

class DogNotFoundException(Excpetion):
    pass

try:
    raise DogNotFoundException()
except DogNotFoundException:
    print("Dog not found!")

# inside
# Dog not found!

With

filename = "/Users/flavio/test.txt"
try:
    file = open(filename, "r")
    content = file.read()
    print(content)
finally:
    file.close()

filename = "/Users/flavio/test.txt"

with open(filename, "r") as file:
    content = file.read()
    print(content)

List compression

numbers = [1, 2, 3, 4, 5]

numbers_power_2 = [n**2 for n in numbers]
# numbers_power_2 = list(map(lambda n: n**2, numbers))

print(numbers_power_2) # [1, 4, 9, 16, 25]