统计学理论学完后，就到了技术部分，包含Python和SQL（使用的是Postgre）
今天先回顾学过的Python部分：
1.Data Types And Operators数据类型和操作符
首先学的是操作符，简单的加减乘除就和普通一样，比较特殊的是
** 求幂运算，简单来说就是次方，3的6次方 3**6
// 向下整数除法 7//2 =3 -7//2=-4
% 求余数
负值是等号，==是判断是否相等
+= -= *=
整数和浮点数
type() 检查参数类型
int(49.7) =49 直接舍去
报错会有两种 Exception 和error
exception是运行时报错
error是运行前，检查出来的错误。
布尔值true false、逻辑运算and or not
接下来是比较重要的难点
字符串string、列表list、元组tuples、set集合、字典 dictionary
| Data Structure | Ordered | Mutable | Constructor | Example |
|---|---|---|---|---|
| int | NA | NA | int() |
5 |
| float | NA | NA | float() |
6.5 |
| string | Yes | No | ' ' or " " or str() |
“this is a string” |
| bool | NA | NA | NA | True or False |
| list | Yes | Yes | [ ] or list() |
[5, ‘yes’, 5.7] |
| tuple | Yes | No | ( ) or tuple() |
(5, ‘yes’, 5.7) |
| set | No | Yes | { } or set() |
{5, ‘yes’, 5.7} |
| dictionary | No | Keys: No | { } or dict() |
{‘Jun’:75, ‘Jul’:89} |
字符串：有序，不可修改
单引号来包含双引号
\ 来转义
+ 来合并字符串，*来复制，没有减法和除法
len()/format()
a.count(b)/a.find(b)
list列表 可排序可改变，使用广泛
names = [“Carol”, “Albert”, “Ben”, “Donna”]
names[0]第一个 ；names[-1]最后一个，[len(string)-1]
month[6:9] 7-9月份，不包含上限。
[:6]前6个元素，不包含7
in 和not in判断
max() 最大的int，字符串首字母靠后的，多重type无法比较-min()
sorted()从下到大排序
sorted(list,reverse=True)从大到小排序
“-“.join(list)连接字符串
b.append(‘one’)添加到列表末尾 直接使用
b=names.pop(1) 提出第二个元素
元组Tuples 包含不可变 有序的数据结构，括号可选
没有append和pop方法
tup1[0] 方括号索引查找
内置4个函数，cmp比较两个元组，max,min和tuple(listname)转化
location = (13.4125, 103.866667)
print("Latitude:", location[0])
print("Longitude:", location[1])元组解包，就是把元组内的参数赋值，下方第二行就是解包
dimensions = 52, 40, 100
length, width, height = dimensions
print("The dimensions are {} x {} x {}".format(length, width, height))
也可以写成
length, width, height = 52, 40, 100
print("The dimensions are {} x {} x {}".format(length, width, height))set 集合 包含唯一元素 且 顺序不定，可以修改
scores=[‘4′,’5′,’6′,’9’]
可以由list生成 set(listname)
set.add(‘newone’)添加元素 没有append() 随机添加到一个位置
set.pop()随机删除一个元素
dictionary 字典 存储的是元素对 key:value，数组的概念
key可以是int string float 不可变的值且统一
elements = {“hydrogen”: 1, “helium”: 2, “carbon”: 6}
print(elements[“helium”])
添加就直接添加 elements[“lithium”] = 3
“some” in elements 检查是否存在于字典
elements .get(“some”) 比直接方括号elements.[“some”]要安全，不存咋的话，也只返回None而不是报错
还可以设置成elements .get(“some”，”There\`s no such key”)来自定义返回语句
Compound Data Structures 应该是python的多维数组
elements = {"hydrogen": {"number": 1,
"weight": 1.00794,
"symbol": "H"},
"helium": {"number": 2,
"weight": 4.002602,
"symbol": "He"}}hydrogen_weight = elements[“hydrogen”][“weight”]
控制流 control flow
IF ELIF ELSE
注意冒号和缩进。
points = 174
points = 174 # use this input when submitting your answer
# set prize to default value of None
prize = None
# use the value of points to assign prize to the correct prize name
if points <= 50:
prize = "wooden rabbit"
elif 151 <= points <= 180:
prize = "wafer-thin mint"
elif points >= 181:
prize = "penguin"
# use the truth value of prize to assign result to the correct message
if prize:
result = "Congratulations! You won a {}!".format(prize)
else:
result = "Oh dear, no prize this time."
print(result)
循环 loop
for和while的使用
usernames = ["Joey Tribbiani", "Monica Geller", "Chandler Bing", "Phoebe Buffay"]
for i in range(len(usernames)):
usernames[i] = usernames[i].lower().replace(" ", "_")
print(usernames)while求阶乘
# Start with a sample number for first test - change this when testing your code more!
number = 6
# We'll always start with our product equal to the number
product = number
# Write while loop header line - how will you tell it when to stop looping?
while number > 1:
# Each time through the loop, what do we want to do to our number?
number -= 1
# Each time, what do we want to multiply the current product by?
product *= number
# Print out final product (how do we indicate this should happen after loop ends?)
print(product)for的方式
# This is the number we'll find the factorial of - change it to test your code!
number = 6
# We'll start with the product equal to the number
product = number
# Write a for loop that calculates the factorial of our number
for num in range(1, number):
product *= num
# print the factorial of your number
print(product)range函数，使用此函数得到list的索引
range(start,stop,step) start 和step默认是1
range(5)只有一个整数时，是stop的值 ，0-4
range(2,10) 是start =2 和stop=10 step默认为1， 2~8
迭代字典
fruit_count, not_fruit_count = 0, 0
basket_items = {'apples': 4, 'oranges': 19, 'kites': 3, 'sandwiches': 8}
fruits = ['apples', 'oranges', 'pears', 'peaches', 'grapes', 'bananas']
#Iterate through the dictionary
for fruit, count in basket_items.items():
if fruit in fruits:
fruit_count += count
else:
not_fruit_count += count
print("The number of fruits is {}. There are {} items that are not fruits.".format(fruit_count, not_fruit_count))
while 是条件为真时继续运行
card_deck = [4, 11, 8, 5, 13, 2, 8, 10]
hand = []
# adds the last element of the card_deck list to the hand list
# until the values in hand add up to 17 or more
while sum(hand) < 17:
hand.append(card_deck.pop())limit = 40
num = 0
while (num+1)**2 < limit:
num += 1
nearest_square = num**2
print(nearest_square)break 和 continue
break终止并跳出循环
continue 跳过本次迭代，而不完全跳出循环
headlines = ["Local Bear Eaten by Man",
"Legislature Announces New Laws",
"Peasant Discovers Violence Inherent in System",
"Cat Rescues Fireman Stuck in Tree",
"Brave Knight Runs Away",
"Papperbok Review: Totally Triffic"]
news_ticker = ""
for headline in headlines:
news_ticker += headline + " "
if len(news_ticker) >= 140:
news_ticker = news_ticker[:140]
break
print(news_ticker)zip and enumerate 打包和枚举
打包可简单理解成多个list拼成字典
x_coord = [23, 53, 2, -12, 95, 103, 14, -5]
y_coord = [677, 233, 405, 433, 905, 376, 432, 445]
z_coord = [4, 16, -6, -42, 3, -6, 23, -1]
labels = ["F", "J", "A", "Q", "Y", "B", "W", "X"]
points = []
for point in zip(labels, x_coord, y_coord, z_coord):
points.append("{}: {}, {}, {}".format(*point))
for point in points:
print(point)
cast_names = ["Barney", "Robin", "Ted", "Lily", "Marshall"]
cast_heights = [72, 68, 72, 66, 76]
cast = dict(zip(cast_names, cast_heights))
print(cast){'Lily': 66, 'Barney': 72, 'Marshall': 76, 'Ted': 72, 'Robin': 68}
枚举 Enumerate
cast = ["Barney Stinson", "Robin Scherbatsky", "Ted Mosby", "Lily Aldrin", "Marshall Eriksen"]
heights = [72, 68, 72, 66, 76]
for i, character in enumerate(cast):
cast[i] = character + " " + str(heights[i])
print(cast)
['Barney Stinson 72', 'Robin Scherbatsky 68', 'Ted Mosby 72', 'Lily Aldrin 66', 'Marshall Eriksen 76']List Comprehensions 列表推导
应该理解成对list的筛选
multiples_3 = [x * 3 for x in range(1, 21)]
print(multiples_3)[3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45, 48, 51, 54, 57, 60]