函数太重要，咱们的程序如果是大厦……好吧……咱们现在的本事只能盖个小趴趴房，那函数就是我们盖房子的石头。
函数有多重要？嗯…从配的图是我美大王瑟兰迪尔就可以看出！
什么是函数？为什么要用函数？
函数是能完成独立功能的模块，有了函数，我们要用其实现的功能，直接调用就可以了，而不用把同样的代码敲两遍三遍四遍。
这不仅大幅减少代码长度，提高代码的利用率，也可以减少出错的几率，隔离错误的影响范围。实现同样功能的重复代码，一个错误，重复代码出现的范围都受波及。
好不容易锁定错误，改动一个，其他都得跟着改，发生遗漏再平常不过。用函数进行模块化，也就把错误困起来，对我们定位查找纠正错误也是大大有益的。
函数还提高程序的可读性，可读性是平常程序宁可牺牲效率也要增加的指标呀！
随着功力的增加，总有一天我们也能写出解决大的复杂问题的程序，学会把大问题敲碎，敲成一个个小问题，然后用函数来实现是必须哒。
在视频中我们讲解了：函数的基础知识，变量的作用域、演示凯撒密码的程序使用函数后的效果、一扫而过python自带模块math里的函数
程序实例：根据用户输入图形用相应函数算出图形面积；用户输入一个数，把这个数以内的素数全部列出来；用户输入任意个数字，函数给出数字之和
函数视频：
# ---------- PROBLEM : SOLVE FOR X ----------
# Make a function that receives an algebraic equation like
# x + 4 = 9 and solve for x
# x will always be the 1st value received and you only
# will deal with addition
# Receive the string and split the string into variables
def solve_eq(equation):
x, add, num1, equal, num2 = equation.split()
# Convert the strings into ints
num1, num2 = int(num1), int(num2)
# Convert the result into a string and join (concatenate)
# it to the string "x = "
return "x = " + str(num2 - num1)
print(solve_eq("x + 4 = 9"))# shape area
import math
def get_area(shape):
# switch the lowercase for easy comparison
shape = shape.lower()
if shape == 'rectangle':
rectangle_area()
elif shape == 'circle':
circle_area()
else:
print("Please enter rectangle or cirle")
# Create function that calculates the rectangle area
def rectangle_area():
length = float(input("Enter the length: "))
width = float(input("Enter the width: "))
area = length * width
print("The area of the rectangle is", area)
# Create function that calculates the circle area
def circle_area():
radius = float(input("Enter the radius: "))
area = math.pi * math.pow(radius, 2)
print("The area of the circle is {:.2f}".format(area))
# Ask the user what shape they want
shape_type = input("Get area for what shape: ")
# Call a function that will route to the correct function
get_area(shape_type)# judge if prime or not
def isprime(num):
for i in range(2, num):
if (num % i) == 0:
return False
return True
# get all primes within numMax
def getPrimes(numMax):
primes = []
for num1 in range(2, numMax):
if isprime(num1):
primes.append(num1)
return primes
maxNum = int(input("Search for primes up to: "))
listOfPrimes = getPrimes(maxNum)
for prime in listOfPrimes:
print(prime, end=', ')
# ---------- PROBLEM : CAESAR'S CIPHER ----------
# Receive a message and then encrypt it by shifting the
# characters by a requested amount to the right
# A becomes D, B becomes E for example
# Also decrypt the message back again
# Cycle through each character in the message
def cipher(befMessage, key):
aftMessage = ''
for char in befMessage:
# if it is a letter
if char.isalpha():
# Get unicode and add the shift amount
char_code = ord(char) + key
# if uppercase
if char.isupper():
# if greater than 'Z'
if char_code > ord('Z'):
char_code -= 26
# if less than 'A'
if char_code < ord('A'):
char_code += 26
# if lowercase
if char.islower():
# if greater than 'z'
if char_code > ord('z'):
char_code -= 26
# if less than 'a'
if char_code < ord('a'):
char_code += 26
# Convert from code to letter and add to message
aftMessage += chr(char_code)
# if not a letter leave the character as is
else:
aftMessage += char
return aftMessage
# Receive the message to encrypt and the number of characters to shift
message = input("Enter your message: ")
key = int(input("How many characters should we shift(-26 ~ 26) "))
secret_message = cipher(message, key)
# print the encrypted message
print("Encrypted message: ", secret_message)
# To decrypt the only thing that changes is the sign of the key
key = -key
orig_message = cipher(secret_message, key)
# print the original message
print("Decrypted message: ", orig_message)# ---------- PROBLEM : CAESAR'S CIPHER ----------
# Cycle through each character in the message
def shift(befMessage, key):
aftMessage = ''
for char in befMessage:
# if it is a letter
if char.isalpha():
# Get unicode and add the shift amount
char_code = ord(char) + key
# if uppercase and greater than 'Z' or lowercase and greater than 'z'
if (char.isupper() and char_code > ord('Z')) or (char.islower() and char_code > ord('z')):
char_code -= 26
# if uppercase and less than 'A' or lowercase and less than 'a'
elif (char.isupper() and char_code < ord('A')) or (char.islower() and char_code < ord('a')):
char_code += 26
# Convert from code to letter and add to message
aftMessage += chr(char_code)
# if not a letter leave the character as is
else:
aftMessage += char
return aftMessage
# Receive the message to encrypt and the number of characters to shift
message = input("Enter your message: ")
key = int(input("How many characters should we shift(-26 ~ 26) "))
secret_message = shift(message, key)
# print the encrypted message
print("Encrypted message: ", secret_message)
# To decrypt the only thing that changes is the sign of the key
key = -key
orig_message = shift(secret_message, key)
# print the original message
print("Decrypted message: ", orig_message)
感谢你对 Python ABC 的支持！