def 函數(shù)名(形參列表):
 #可執(zhí)行語(yǔ)句
 return 返回值

# 函數(shù)定義
def myfunc(arg1, arg2, arg3=None):
 ''' 
 This is a example for python documentation.
 這是一個(gè)為python函數(shù)提供文檔的例子。
 arg1: 第一個(gè)參數(shù)的說(shuō)明
 arg2: 第二個(gè)參數(shù)的說(shuō)明
 arg3: 第三個(gè)參數(shù)的說(shuō)明（這個(gè)參數(shù)有默認(rèn)值）
 v1, v2, v3: 返回值的說(shuō)明 
 '''
 v1 = arg1 + arg2
 v2 = arg1 * arg2
 if arg3 is None:
  v3 = arg1 + arg2
 else:
  v3 = arg1 + arg2 + arg3
 return v1, v2, v3
# 函數(shù)調(diào)用
v1, v2, v3 = myfunc(5, 3, arg3=4)
print(v1, v2, v3) #8 15 12
# 使用arg3的默認(rèn)值調(diào)用函數(shù)
v1, v2, v3 = myfunc(5, 3)
print(v1, v2, v3) #8 15 8
# 忽略一個(gè)返回值
v1, v2, _ = myfunc(5, 3)
print(v1, v2, v3) #8 15 8
# 看看返回值是元組tuple，在返回的過(guò)程中被自動(dòng)解包
print(type(myfunc(5,3))) #<class 'tuple'>

#舉一個(gè)小栗子，計(jì)算紙箱子的體積
def cube_volume(length, width, height = 0.25):
 '''
 計(jì)算紙箱子的體積(單位：m)
 length: 長(zhǎng)； width: 寬
 height: 高（默認(rèn)參數(shù)0.25）
 v: 返回值，紙箱的體積，單位m**3
 '''
 if length <= 0:
  print('length must larger than 0!')
  return 0
 if width <= 0:
  print('width must larger than 0!')
  return 0
 if height <= 0:
  print('height must larger than 0!')
  return 0
 v = length*width*height
 print('length = %.2f; width = %.2f; height = %.2f; cube volume = %.2f' % \
 (length, width, height, v))
 return v
# 使用位置參數(shù)調(diào)用
v = cube_volume(1, 2, 3)
# 使用關(guān)鍵字參數(shù)調(diào)用
v = cube_volume(width = 1, height = 2, length = 3)
# 位置參數(shù)和關(guān)鍵字參數(shù)混用
v = cube_volume(1, height = 2, width = 3)
# 關(guān)鍵字參數(shù)在位置參數(shù)之前會(huì)報(bào)錯(cuò)
# v = cube_volume(width = 1, 2, 3)

# 對(duì)列表的乘方運(yùn)算
def pow_list(x, p):
 '''
 power of a list
 x: list
 p: power
 not return value
 '''
 for i in range(len(x)):
  x[i] **= p
 #這樣會(huì)輸出乘方后的值，但不會(huì)改變x列表里的值
 #因?yàn)樵谟?jì)算時(shí)將x中的值傳入了新的參數(shù)進(jìn)行計(jì)算
 #for i in x:
 # i **= p
 # print(i)
 #print(x)
x = [1,2,3,5,7,9,10,12]
pow_list(x,2)
print(x)
# 可見(jiàn)函數(shù)內(nèi)部對(duì)列表x中元素的更改，當(dāng)函數(shù)退出之后依然有效

# 隱藏的參數(shù)記錄器
def growing_list(x, y=[]):
 y.append(x)
 print(y)
# 重復(fù)執(zhí)行g(shù)rowing_list(‘a(chǎn)')會(huì)發(fā)生什么結(jié)果？
growing_list(2)#[2]
growing_list('張三') #[2, '張三']
growing_list(22333)  #[2, '張三', 22333]

# 不定個(gè)數(shù)的數(shù)字求和
def my_sum(*t):
 # 帶星號(hào)的輸入?yún)?shù)被當(dāng)作元組處理
 print(t, type(t))
 sum = 0
 for s in t:
  sum += s
 return sum
# 事實(shí)上該函數(shù)接受了不定個(gè)數(shù)的輸入?yún)?shù)
my_sum(1,2,3,4,2233)

# 不定個(gè)數(shù)的數(shù)字乘方后求和
def pow_sum(*t, p):
 # 帶星號(hào)的輸入?yún)?shù)被當(dāng)作元組處理
 print(t, type(t))
 sum = 0
 for s in t:
  sum += s**p
 return sum
# 最后一個(gè)參數(shù)p，需要指定關(guān)鍵字傳遞
pow_sum(1,2,3,4,2233,p=2)
# 如果不指定關(guān)鍵字傳遞呢？會(huì)報(bào)錯(cuò)
# pow_sum(1,2,3,4,2233,2)

# 不定個(gè)數(shù)的數(shù)字加權(quán)求和
# 權(quán)重隨著數(shù)字的個(gè)數(shù)而發(fā)生變化
def weighted_sum(x1,x2,*y):
 sum = 0
 n = len(y)
 weight = 1/3/n
 for i in y:
  sum += weight*i
 return sum+1/3*x1+1/3*x2
weighted_sum(1,2,3)
weighted_sum(1,2,3,22,44,55)
weighted_sum(1,2,3,4,5,6)

# 測(cè)試一星參數(shù)和兩星參數(shù)
def test_star(a, b, c, *onestar, **twostar):
 print('a = %d; b = %d; c = %d' % (a, b, c))
 print(onestar, type(onestar))
 print(twostar, type(twostar))
test_star(1, 2, 3, 4, 5, 6, s1 = 7, s2 = 8, s3 = 9)
# 換個(gè)順序呢？
# test_star(1, 2, 3, 4, 5, 6, s1 = 7, s2 = 8, s3 = 9, a = 10, b = 11, c = 12)
# 報(bào)錯(cuò)了，二星參數(shù)后面不能再傳遞關(guān)鍵字參數(shù)了（當(dāng)然位置參數(shù)也不行）

# 如果有默認(rèn)參數(shù)，要注意可能引起的bug
def test_star(a, b, c, p = 5, *onestar, **twostar):
 print('a = %d; b = %d; c = %d; p = %d' % (a, b, c, p)) #a = 1; b = 2; c = 3; p = 4
 print(onestar, type(onestar))#(5, 6) <class 'tuple'>
 print(twostar, type(twostar))#{'s1': 7, 's2': 8, 's3': 9} <class 'dict'>
# 會(huì)傳遞一個(gè)p=4進(jìn)去，而不是設(shè)想的，onestar=(4,5,6)
test_star(1, 2, 3, 4, 5, 6, s1 = 7, s2 = 8, s3 = 9)

# 炸參數(shù)例子
def zha(a,b,c):
 print(a,b,c)
# 炸元組
z = (1,2,3)#1 2 3
zha(*z)
# 炸列表
z = [4,5,6]#4 5 6
zha(*z)
# 炸字典
z = {'a':7,'b':8,'c':9} #7 8 9
zha(**z)
# 炸字典
z = {'c':7,'a':8,'b':9} #8 9 7
zha(**z)
# 如果炸開(kāi)后參數(shù)個(gè)數(shù)或Key不匹配，會(huì)報(bào)錯(cuò)
# z = {'c':7,'a':8}
# zha(**z)

# 傳遞數(shù)值類(lèi)型參數(shù)
# 在函數(shù)內(nèi)修改，在函數(shù)外面不受影響
def mod_para1(a,b):
 print('In mod_para1, before modification: a = %d; b = %d' % (a,b)) #a = 2; b = 8
 a *= 2
 b += 4
 print('In mod_para1, after modification: a = %d; b = %d' % (a,b)) #a = 4; b = 12
a = 2
b = 8
print('Out of mod_para1, before modification: a = %d; b = %d' % (a,b)) #a = 2; b = 8
mod_para1(a,b)
print('Out of mod_para1, after modification: a = %d; b = %d' % (a,b)) #a = 2; b = 8

# 列表通過(guò)函數(shù)傳參時(shí)，被改動(dòng)了數(shù)據(jù)
def mod_para2(x):
 print('In mod_para2, before modification: x = ' + str(x))
 for i in range(len(x)):
  x[i] *= 2
 print('In mod_para2, after modification: x = ' + str(x))
x = [i for i in range(10)]
print('Out of mod_para2, before modification: x = ' + str(x))
mod_para2(x)
print('Out of mod_para2, after modification: x = ' + str(x))
import copy
A = [1,2,3]; B = copy.copy(A)
mod_para2(B); print(A,B)

gv1 = 1
def test():
 # gv1=2
 print('在函數(shù)內(nèi)部訪問(wèn)全局變量：gv1 = %d' % gv1) #1
 # gv1=2
test()
print('在函數(shù)外部訪問(wèn)全局變量：gv1 = %d' % gv1) #1

# 訪問(wèn)被遮蔽的全局變量
gv1 = 1
def test():
 # 用globals函數(shù)訪問(wèn)被遮蔽的全局變量
 print('在函數(shù)內(nèi)部訪問(wèn)全局變量：gv1 = %d' % globals()['gv1'])
 gv1 = 2 
 print('在函數(shù)內(nèi)部訪問(wèn)修改后的全局變量：gv1 = %d' % gv1)
test()
print('在函數(shù)外部訪問(wèn)全局變量：gv1 = %d' % gv1) # 函數(shù)內(nèi)部修改的其實(shí)是同名局部變量，全局變量沒(méi)有被修改。

# 測(cè)試全局變量
gv1 = 1
def test():
 global gv1 #全局變量我來(lái)?yè)慰? print('在函數(shù)內(nèi)部訪問(wèn)全局變量：gv1 = %d' % gv1) #1
 gv1+=1
test()
print('在函數(shù)外部訪問(wèn)全局變量：gv1 = %d' % gv1) #2

# 利用局部函數(shù)實(shí)現(xiàn)多種平均值的切換
def mymean(x, mtype = 'arithmetic'):
 '''計(jì)算列表x的平均值，用mtype定義計(jì)算哪種平均值，默認(rèn)為算術(shù)平均值（arithmetic mean） '''
 def arithmetic(x): 
  ''' 算術(shù)平均值（arithmetic mean)  '''
  m = sum(x)/len(x); return m
 def geometric(x): 
  '''幾何平均值（geometric mean） '''
  p = 1.;  n = len(x)
  for i in range(n):p *= x[i]
  m = p ** (1/n); return m
 def harmonic(x): 
  ''' 調(diào)和平均值（harmonic mean) '''
  s = 0.;n = len(x)
  for i in range(n):  s += 1/x[i]
  m = 1/(s/n);  return m
 if mtype == 'arithmetic': return arithmetic
 elif mtype == 'geometric': return geometric
 elif mtype == 'harmonic':  return harmonic
 else:  return arithmetic

# 局部函數(shù)內(nèi)的變量與函數(shù)內(nèi)的局部變量相沖突，這個(gè)程序會(huì)報(bào)錯(cuò)
def test1():
 fv = 1
 def test2():
  # print('局部函數(shù)內(nèi)打印上層函數(shù)中的局部變量：%d' % fv) # 會(huì)在這里報(bào)錯(cuò)
  fv = 2
  print('局部函數(shù)內(nèi)打印上層函數(shù)中的局部變量（更改后）：%d' % fv) #2  
 test2()
 print('上層函數(shù)內(nèi)打印局部變量（更改后）：%d' % fv) #1  
 return fv
print('上層函數(shù)外打印局部變量（更改后）：%d' % test1()) #1

# 局部函數(shù)內(nèi)的變量與函數(shù)內(nèi)的局部變量相沖突，應(yīng)該改成這樣就不報(bào)錯(cuò)了
def test1():
 fv = 1
 def test2():
  nonlocal fv # 用nonlocal聲明，把fv聲明為上一層函數(shù)的變量
  print('局部函數(shù)內(nèi)打印上層函數(shù)中的局部變量：%d' % fv) #1
  fv = 2
  print('局部函數(shù)內(nèi)打印上層函數(shù)中的局部變量（更改后）：%d' % fv) #2 
 test2()
 print('上層函數(shù)內(nèi)打印局部變量（更改后）：%d' % fv) #2
 return fv
print('上層函數(shù)外打印局部變量（更改后）：%d' % test1()) #2

# 以第三章栗子中mymean函數(shù)為例
# 將函數(shù)賦值給變量f
f = mymean2('arithmetic')
# 打印出來(lái)看看
print(f)
# 測(cè)試一下
x = list(range(1,10))
m = f(x)
print(m)
# 也可以像上面的例子一樣，連起來(lái)寫(xiě)
print(mymean2('geometric')(x))

# 以第三章栗子中mymean函數(shù)為例
# 編寫(xiě)另一個(gè)程序，對(duì)列表中的數(shù)字進(jìn)行變換，變成均值為1的另一個(gè)列表
# 均值，可以是算術(shù)平均值、幾何平均值、調(diào)和平均值
def mynormalize(x, mtype):
 f = mymean(mtype)
 m = f(x)
 return [i/m for i in x]
x = list(range(1,10))
mtype = 'geometric'
print(mymean(mtype)(x))
print(mynormalize(x, mtype))

# 斐波那契數(shù)列（Fibonacci sequence）
# 在現(xiàn)代物理、準(zhǔn)晶體結(jié)構(gòu)、化學(xué)等領(lǐng)域，斐波納契數(shù)列都有直接的應(yīng)用
def Fibonacci(n):
 ''' Fibonacci sequence
 f(0)=1, f(1) = 1, f(n) = f(n-1)+f(n-2) '''
 if n == 0 or n == 1:  return 1
 else:return Fibonacci(n-1) + Fibonacci(n-2)
# 測(cè)試一下，注意n不要設(shè)的太大，python的遞歸效率是比較低的，太大會(huì)死機(jī)
print(Fibonacci(5))
# 斐波那契數(shù)列，前20位
print('Fibonacci sequence:')
for i in range(20):
 print('%d: %d' % (i,Fibonacci(i)))

# 一行中的hello world
greeting = lambda: print('Hello lambda!')
greeting()
# lambda表達(dá)式可以放在數(shù)組里面，批量運(yùn)行
L = [lambda x: x**2, lambda x: x**3, lambda x: x**4]
for p in L:
 print(p(3))

# 用lambda表達(dá)式代替局部函數(shù)
def mymean2(mtype = 'arithmetic'):
 ''' 返回計(jì)算平均值所用的函數(shù)，用mtype定義計(jì)算哪種平均值，默認(rèn)為算術(shù)平均值（arithmetic mean） '''
 # 由于lambda表達(dá)式只能寫(xiě)一行，這里用numpy和scipy的現(xiàn)成的函數(shù)來(lái)實(shí)現(xiàn)
 import numpy as np
 import scipy.stats as st
 a = np.array(x)
 if mtype == 'arithmetic': # 算術(shù)平均值（arithmetic mean）
  return lambda a: np.mean(a)
 elif mtype == 'geometric':# 幾何平均值（geometric mean）
  return lambda a: st.gmean(a)
 elif mtype == 'harmonic': # 調(diào)和平均值（harmonic mean）
  return lambda a: st.hmean(a)
 else:  # 默認(rèn)：算術(shù)平均值（arithmetic mean）
  return lambda a: np.mean(a)
x = list(range(1,10))
print(x)
print(mymean2('arithmetic')(x))
print(mymean2('geometric')(x))
print(mymean2('harmonic')(x))

# 判斷所有元素是否為T(mén)rue，相當(dāng)于多重的and
help(all)
print(all([3>2,6<9]))
# 任意一個(gè)元素是否為T(mén)rue，相當(dāng)于多重的or
help(any)
print(any([3>2,6<9]))
# 最大值和最小值
help(max)
help(min)
print(max([1,2,5,3]))
print(min([1,2,5,3]))
# 四舍五入(到小數(shù)點(diǎn)后第n位)
help(round)
print(round(3.1415926,3))
# 所有元素相加 
help(sum)
print(sum([1,2,3]))
print(sum([1,2,3],5))
# 乘冪
help(pow)
print(pow(6,2))
print(pow(6,2,5))
# 帶余除法
help(divmod)
print(divmod(6,2))
# 絕對(duì)值
help(abs)
print(abs(-2.56))