代碼格式

強制縮進

• Python開發者有意讓違反了縮進規則的程序不能通過編譯，以此來強制程序員養成良好的編程習慣。并且Python語言利用縮進表示語句塊的開始和退出（Off-side規則），而非使用花括號或者某種關鍵字。增加縮進表示語句塊的開始，而減少縮進則表示語句塊的退出。縮進成為了語法的一部分。
• 根據PEP的規定，必須使用4個空格來表示每級縮進。

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基本語法

• 弱類型
• 變量必須先賦值再使用
• 小心引用
• 2和3的常見差異
  
  • xrange
  • print
  • 數據類型統一，取消unicode和long
  • utf8: 3.x代碼默認utf-8

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# 變量必須先賦值再使用
a = 1234
print(a)
a = 'abcd'
print(a)

try:
    print(b)
except Exception as e:
    print(e)

#傳值使用的是引用
a = [1, 2, 3 , 4]
def func(a):
    a[0] = 2

func(a)
print(a)

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關鍵字

• 常量

  True False None
  

• 對象與容器

  class import from del
  

• 邏輯操作

  and or not
  

• 函數

  def return
  

• 判斷與循環控制

  if elif else
  is
  in
  assert
  for while continue break
  

• 異常

  raise try except finally
  with as
  

• 作用域

  global nonlocal
  

• 匿名函數與協程

  yield lambda
  

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循環判斷

• 注意加“:”
• 沒有do-while循環
• 沒有switch
• break是中斷整個循環
• continue是結束本次迭代進入下一個

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score = 80
if score > 90:
    print('A')
elif score > 70:
    print('B')
elif score >= 60:
    print('C')
else:
    print('D')

total = 0
i = 1
while i <= 100:
    total += i
    i += 1  # 沒有++i或者--i
print(total)

'''
for循環只作用于容器！！！
沒有這種寫法：
  for (i = 0; i < 100; ++i):
      # TODO
上面這種循環只能用while實現
'''

i = 0
while i < 3:
    j = 0 
    while j <= 3:
        if j == 2:
            j += 1
            continue  # 又去了while j <= 3
        print(i, j)
        j += 1
    i += 1

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函數

• def定義函數
• 默認參數
• 名字參數
• 函數也是對象
• 函數式編程簡介：map/reduce/lambda

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def hello(who = 'world'):
    print('hello %s!' % (who))

hello()
hello('sea')

# f(x) = x * 5 + 100
# g(x) = x * 5; f(x) = x + 100
# => f(g(x)) = x * 5 + 100
def g(x):
    return x * 5
def f(gf, x):
    return gf(x) + 100
print(f(g, 100))
print(f(lambda x: x * 5, 100))

def f(gf, x, y):
    return gf(x, y) + 100
print(f(lambda x, y: x * y, 100, 200))

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容器

list：數組

# list就是數組

li = [1, 2, 3, 4, 5]
# 遍歷
for i in li:
    print(i)
print("--------------------")

# 用range模擬for (i = 0; i < x; ++i)
# range(x) => [0, x - 1]
# range(x, y) => [x, y - 1]
# range(x, y, z) => [x, x + z,..., < y]
for i in range(len(li)):
    print(li[i])
print("--------------------")

for i in range(1, 10, 2):
    print(i)

print("--------------------")

# 負數索引
print(li[-1])
print(li[-2])
print("--------------------")

# 負數step的range => [x, x - z, ..., > z]
for i in range(3, -1, -1):
    print(i)
print("--------------------")

# 添加元素
li = []
li.append(1)
li.append(2)
li.append('abc')
li.append(['d', 'e', 'f'])
print(li)
print("--------------------")

# 按元素添加數組
li = [1, 2]
li_2 = [3, 4, 5]
# 我們想要[1, 2, 3, 4, 5]
# li.append(li_2) => [1, 2, [3, 4, 5]]
li.extend(li_2)
print(li)
print("--------------------")

# 刪除元素
li.pop()    # => [1, 2, 3, 4]
print(li)
print("--------------------")
li.pop(2)   # => [1, 2, 4]
print(li)
print("--------------------")

li = [5, 8, 7, 4, 2, 3]
li.sort()
print(li)
print("--------------------")

# lambda幫助排序
li = [[5, 2], [3, 8], [2, 11], [7, 6]]
# li.sort(key = lambda x: x[0]) # 參數名字
# 與lamda等價寫法
def item_key(x):
    return x[0]
li.sort(key = item_key)
print(li)

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tuple：只讀數組

# 只讀數組
tp = (1, 2, 3)
try:
    tp[0] = 100
except Exception as e:
    print(e)

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set：沒有重復元素的數組

# 去重的數組
s = set([1, 2, 2, 3, 3, 4, 5])
print(s)
s = set((2, 3, 4, 5, 6, 2, 1, 9))
print(s)

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dict：字典（哈希表）

# key<->value對應的hash表
di = {'k1': 'v1', 'k2': 'v2'}
di['k3'] = 'v3'
di['k4'] = 'v4'

for k in di:
    print(di[k])

for k, v in di.items():
    print(k, v)

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數組切片

# [1, 2, 3, 4, 5]
#  => [1, 2, 3]
#  => [3, 4]
li = [1, 2, 3, 4, 5]
li_0_2 =li[0:3] # 0 <= ? < 3
# 等價li[:3]
print(li_0_2)
# [start, end, step] => [start, start + step, ..., < end]
# start默認是0，end默認-1，step默認1
li_last_3 = li[-1:-4:-1]
print(li_last_3)

# 直接用切片反轉數組
print(li[::-1])
print(li[-2::-1])

# 切片是復制
li_0_2[-1] = 100
print(li)

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字符串與數組的關系

s = 'abcdefg'
try:
    str[0] = 'x'
except Exception as e:
    print(e)

# 修改字符串
li = list(s)
# print(li)
li[0] = 'x'
s = ''.join(li)
print(s)
s = '-'.join(li)
print(s)

# 切割
s = 'abc,def,ghi'
p1, p2, p3 = s.split(',')
print(p1, p2, p3)

# 下標訪問和切片
s = 'abcdefg'
print(s[0], s[-1])
print(s[2:5])

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面向對象

• 一切皆對象
• 獲取對象信息：type和dir
• class聲明對象
• 重要的self
• 繼承與多態（什么是鴨子類型？）

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# 用type查看對象類型
print(type([1, 2, 3, 4]))
print(type('abcd'))
print(type({1:2, 2:3}))
print("------------------")

# 用dir查看屬性和方法
print(dir(list))
print("------------------")

class Clazz(object):
    # self參考C++的this指針
    def __init__(self, x, y):
        self.x = x
        self.y = y

    # 聲明成員函數的時候，第一個參數一定是self，不要忘記
    def display(self):
        print(self.x, self.y)

print(type(Clazz))
print("------------------")

clz = Clazz(100, 200)
clz.display()  # => display(clz)

class Base:
    def run(self):
        print('Base::run')

class Tom(Base):
    def run(self):
        print('Tom::run')

t = Tom()
print(isinstance(t, Base))
print("------------------")
t.run()


# 鴨子類型
def run(runner):
    runner.run()

class R1:
    def run(self):
        print('R1::run')

class R2:
    def run(self):
        print('R2::run')

run(R1())
run(R2())

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文件讀寫

• 文本文件讀寫

with open('text.txt') as f:
    for line in f.readlines():
        print(line)

with open('text.txt') as f:
    while True:
        line = f.readline()
        if not line:
            break
        print(line)

• 二進制文件讀寫

with open('text.txt', 'rb') as f:
    print(f.read())

• string與bytes

s = 'abcdefg'
b = bytes(s)
print(b)

• 文件和目錄操作

import os
#遍歷文件夾下的所有文件
for x in os.listdir("D:\\螞蟻眾包\\20180609"):
    file_path = "%s\\%s"%("D:\\螞蟻眾包\\20180609",x)
    #判斷是否是文件夾
    if os.path.isdir(file_path):
        print(file_path,"is a dir.")
    #判斷是否是文件
    elif os.path.isfile(file_path):
        print(file_path,"is a file.")
    else:
        print(file_path,"is not a dir or file.")

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多線程

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import threading

def thread_func(x):
    # 自己加sleep和其它復雜操作看效果
    print('%d\n' % (x * 100))

threads = []
for i in range(5):
    threads.append(threading.Thread(target = thread_func, args = (100, )))

for thread in threads:
    thread.start()

for thread in threads:
    thread.join()

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錯誤和異常處理

# 錯誤處理

import logging

try:
    r = 10 / 0
except ZeroDivisionError as e:
    print(type(e))
    print(e)
finally:
    # 主要防止資源泄露！
    print('Always come here.')

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