1 Variables and simple data types
Variable naming format: variable name = "assignment"
1.1 Variable usage specification
When using variables, some rules need to be followed. Violation of these rules will cause errors.
~ Variable names can only contain numbers, letters, and underscores. Variable names cannot start with a number and cannot contain spaces.
~ Variable names cannot use Python reserved words and function names as variable names. Such as print
The following is a list of 33 reserved words in python3:
~ Variable names should be simple and descriptive. If name is better than n, user_name is better than u_n.
~ Use capital letters I and O carefully to avoid mistakenly interpreting the numbers 1 and 0.
1.2 String
A string is a series of characters. In Python, all quotation marks are strings, and the quotation marks include single and double quotation marks. This flexibility can include quotation marks and apostrophes in the string, such as:
>>> str = "I'm David"
>>> str1 = 'I told my friend,"i love Python"'Common string manipulation methods
Display each word in capital letters:
>>> name = "hello python world"
>>> print(name.title())
Hello Python WorldChange the string to all uppercase or all lowercase:
>>> str1 = "I love python"
>>> print(str1.upper()) #将字符串改为全部大写
I LOVE PYTHON
>>> print(str1.lower()) #将字符串改为全部小写
i love pythonString concatenation (splicing)
Python uses the plus sign (+) to combine strings, such as:
>>> first_name = "Guido"
>>> last_name = "van Rossum"
>>> full_name = first_name + " " + last_name
>>> print(full_name)
Guido van RossumUse tab characters \t or newline characters\n to add white space:
>>> print("Languages:\n\tPython\n\tC++\n\tPHP")
Languages:
Python
C++
PHPRemove spaces in a string:
>>> name = " p y t h o n "
>>> print(name.rstrip()) #删除字符串右端空格
p y t h o n
>>> print(name.lstrip()) #删除字符串左端空格
p y t h o n
>>> print(name.strip()) #删除字符串两端空格
p y t h o n
>>> print(name.replace(' ','')) #删除字符串全部空格包括制表符和换行符
python
Many people learn python and don't know where to start.
Many people learn python and after mastering the basic grammar, they don't know where to find cases to get started.
Many people who have done case studies do not know how to learn more advanced knowledge.
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Serial number of the string
A string is a sequence of characters, which can be indexed according to a single character or character fragments.
>>> name = "Hello World"
>>> print(name[0])
H
>>> print(name[0:-1])
Hello Worl
>>> print(name[-1])
d
>>> print(name[::])
Hello World
>>> print(name[0:11])
Hello WorldFind the lowest character index number in the string: S.find(sub [,start [,end]]) -> int
Return -1 on failure
>>> name = "hello world"
>>> print(name.find('d'))
10Return the number of occurrences of certain characters: S.count(sub[, start[, end]]) -> int
>>> name = "hello world"
>>> print(name.count('l'))
3Return a list of strings by the separator: S.split([sep [,maxsplit]]) -> list of strings, if maxsplit is given, the maximum is maxsplit
>>> name = "hello world"
>>> print(name.split(' '))
['hello', 'world']
>>> print(name.split(' ',0))
['hello world']String formatted output (format and% usage)
% Method format code
>>> "{}:计算机{}的CPU占用率为{}%".format('2019-03-25','python',10) #S.format(*args, **kwargs) -> string '2019-03-25:计算机python的CPU占用率为10%' >>> "%s:计算机%s的CPU占用率为%d%%" % ('2019-03-25','python',10) #%用法 '2019-03-25:计算机python的CPU占用率为10%
Summary: You can use the help function to view string related operations, such as help(str.find)
2 Combined data type
2.1 Collection type
Definition and operation of collection
~ The collection is represented by curly braces {}, and the elements are separated by commas;
~Create a collection type with {} or set();
~ To create an empty collection type, you must use set();
~ Disorder between collection elements;
~Each element in the collection is unique, no identical elements exist
>>> A = {"python",'666',("wenwei-blog",666)}
{'python', '666', ('wenwei-blog', 666)}
>>> B = set("pypy")
{'y', 'p'}
>>> C = {"python",123,"python",123}
{'python', 123}Set operator
6 operators
4 enhanced operators
Collection operation method
Collection application scenarios
Containment relationship comparison; data deduplication.
2.1 Sequence type definition
~Sequence is a set of elements with a sequential relationship
~ Sequence is a base type (basic data type)
~Sequence types are divided into string, list, and tuple types
2.2 List of sequence types
The list is composed of a series of elements arranged in a specific order, and square brackets [] are used to indicate the list.
Add, delete, modify and check related operations on the list
| Function or method |
description |
Instance |
| L[i]=x |
Replace the ith data item of the list L as x |
>>> L = ['Python','PHP','JavaScript','C++'] >>> L[1] = 'Java' >>> L ['Python', 'Java', 'JavaScript', 'C++'] |
| L[i:j]=L1 |
Replace the data of items i to j in list L with list L1 |
>>> L |
| of L [i: j: k] |
Delete the data of items i to j in the list L with k as the number of steps |
>>> L |
| L+=L1 or L.extend(L1) |
Add elements of list L1 to list L |
>>> L;L1 ['C', 'JavaScript', 'Java', 'Ruby', 'Lua'] |
| L*=n |
Repeat the elements of the L list n times |
>>> L1*=2 |
| L.append(x) |
It is better to add element x to the L list |
>>> L |
| L.clear() |
Delete all elements of list L |
>>> L |
| L1 = L.copy() |
Copy the L list to generate a new L1 list |
>>> L |
| L.insert(i,x) |
在列表L的第i位置增加元素x |
>>> L |
| L.pop(i) |
将列表L中的第i项元素删除 |
>>> L;L.pop(2); |
| L.remove(x) |
将列表的第一个x元素删除 |
>>> L |
| L.reverse(x) |
将列表L中的元素反转 |
>>> L;L.reverse();L |
| L.sort () |
Sort the elements of list L in alphabetical order |
>>> L.sort() |
| L.index(x) |
Get the index number of the x element of the list L |
>>> L.index('Python') |
Perform simple statistical calculations on list numbers
>>> digits = [1,23,434,55,44,67]
>>> min(digits)
1
>>> max(digits)
434
>>> sum(digits)
624List related exercises
Exercise 1: Create a list containing the numbers 1-100 and print it out and then calculate the total value of the list numbers.
>>> digits = [value for value in range(1,101)];sum(digits)
5050Exercise 2: Find odd numbers from 1-20
>>> for i in range(1,21,2):
print(i)
1
3
5
7
9
11
13
15
17
19Exercise 3: Output numbers within 3-30 that are divisible by 3
>>> lists = [n for n in range(3,31)]
>>> lists
[3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30]
>>> for i in lists:
if i % 3 == 0:
print(i)
3
6
9
12
15
18
21
24
27
302.3 Tuples of sequence types
A tuple is actually similar to a list. It also stores a set of data, but once it is created, it cannot be modified, so it is also called a read-only list.
It has only two methods, one is count (to count the number of times an element of a tuple appears, tuple.count('str')), and the other is index (to view the index number of an element tuple.index('str'))
>>> names = ('zhiwenwei','zhouyouxian')
>>> names.index('zhiwenwei')
0
>>> names.count('zhiwenwei')
1Tuple exercises
There are the following variables, please implement the required function
tu = ("alex", [11, 22, {"k1": 'v1', "k2": ["age", "name"], "k3": (11,22,33)}, 44])
a. Can the first element "alex" in the tu variable be modified?
Tuples cannot be modified directly, they need to be converted into lists or dictionaries
b. What type of value corresponds to "k2" in the tu variable? Can it be modified? If you can, please add an element "Seven"
k2 is the key of the dictionary, and the corresponding value is the list can be modified: tu[1][2]['k2']='Seven'
c. What type is the value of "k3" in the tu variable? Can it be modified? If you can, please add an element "Seven"
k3 is the key of the dictionary, and the corresponding value is a tuple that cannot be modified
Many people learn python and don't know where to start.
Many people learn python and after mastering the basic grammar, they don't know where to find cases to get started.
Many people who have done case studies do not know how to learn more advanced knowledge.
For these three types of people, I will provide you with a good learning platform, free to receive video tutorials, e-books, and course source code!
QQ group: 553215015
2.4 Dictionary type
A dictionary is a collection of 0 or more key-value pairs, with no length limit, and can be based on the content of the key index value.
In the Python language, the mapping is realized through a dictionary, which is established through braces {}, and the model is as follows:
{键1：值1，键2：值2，...}
>>> city = {'中国':'北京','美国':'纽约','法国':'巴黎'}
>>> city
{'中国': '北京', '美国': '纽约', '法国': '巴黎'}拓展：字典是无序的。python语言中，字符串、列表、元组都是采用数字索引，字典采用字符索引。
字典的函数和方法
字典的基本原则
字典是一个键值对的集合，该集合以键为索引，一个键对应一个值信息
字典中的元素以键信息为索引访问
字典长度是可变的，可以通过对键信息赋值实现增加或修改键值对。
2.5 jieba库基本介绍
jieba库提供三种分词模式，最简单只需要掌握一个函数；
jieba是优秀的中文分词第三方库，需额外安装
jieba库的安装方法
pip install jiebajieba分词的三种模式
精确模式：把文本精确切分，不存冗余单词
>>> word1 = jieba.lcut("python无所不能！除了生不出孩子,我们应该学习使用它！")
Building prefix dict from the default dictionary ...
Dumping model to file cache /tmp/jieba.cache
Loading model cost 1.832 seconds.
Prefix dict has been built succesfully.
>>> print(word1,type(word1))
['python', '无所不能', '！', '除了', '生不出', '孩子', ',', '我们', '应该', '学习', '使用', '它', '！'] <class 'list'>2.6 实例：文本词频统计
英文文本：hamlet，统计出现最多的英文单词
https://python123.io/resources/pye/hamlet.txt
代码实现：
#Hamlet词频统计
def getText():
txt = open("hamlet",'r').read()
txt = txt.lower() #大写字母转换小写
for word in '~!@#$%^&*()_+-={}[],./:";<>?':
txt = txt.replace(word," ")#把多余符号转换为空格
return txt
hamletTxt = getText()
words = hamletTxt.split() #以空格拆分为列表
counts = {}
for word in words:
counts[word] = counts.get(word,0) + 1 #以每个词为键，值默认0，,每出现一次累加1
items = list(counts.items())
items.sort(key=lambda x:x[1],reverse=True) #[1]按照第二维排序，reverse=True表示降序
for i in range(10):
word,count = items[i]
print("{0:<10}{1:5}".format(word,count))中文文本：三国，分析人物
https://python123.io/resources/pye/threekingdoms.txt
import jieba
txt = open("Threekingdoms", 'r', encoding="utf-8").read()
excludes = {'将军','却说','荆州','二人','不可','不能','如此'}
words = jieba.lcut(txt)
counts = {}
for word in words:
if len(word) == 1:
continue
#书中同一人物多个名字统一改为一个名字
elif word == '诸葛亮' or word == '空明日':
rword = "孔明"
elif word == '关公' or word == '云长':
rword = "关羽"
elif word == '玄德' or word == '玄德日':
rword = "刘备"
elif word == '孟德' or word == '丞相':
rword = "曹操"
else:
rword = word
counts[word] = counts.get(word, 0) + 1
for word in excludes:
del counts[word] #去重
items = list(counts.items())
items.sort(key=lambda x:x[1],reverse=True)
for i in range(10):
word,count = items[i]
print("{0:<10}{1:>5}".format(word,count))3 程序的控制结构
3.1 程序的分支结构
根据判断条件结果而选择不同向前路径的运行方式
单分支结构
if <条件> :
<语句块>
示例：
guess = eval(input("请输入数字："))
if guess == 88:
print("猜对了")二分支结构
if <条件> :
<语句块>
else：
<语句块>guess = eval(input("请输入数字："))
if guess == 88:
print("猜对了")
else:
print("猜错了")多分支结构
if <条件1> :
<语句块1>
elif <条件2> :
<语句块2>
...
else:
<语句块N>
示例
age = 25
count = 0
while count < 3:
guess_age = int(input("guess_age:"))
if guess_age == age:
print("yes,you got it!!!")
break
elif guess_age > age:
print("think smaller...")
else:
print("think bigger...")
count += 1
3.2 程序的循环结构
遍历循环
语法结构：
for <循环变量> in <循环结构>:
<语句块>
无限循环
由条件控制的循环运行方式
语法结构：
while <条件>:
<语句块>
循环控制保留字
break 和 continue
-break 跳出并结束当前整个循环，执行循环后的语句
-continue 结束当次循环，继续执行后续次数循环
循环的拓展
当循环没有被break语句退出时，执行else语句。
else语句作为“正常”完成循环的奖励
3.3 异常处理
异常处理的基本使用
示例
try:
num = eval(input("请输入数字"))
print(num**2)
except:
print("你输入的不是数字")异常处理的高级使用
try：
语句块1
except：
语句块2
else：
语句块3（不发生异常时执行）
finally
语句块4（最终会执行）
3.4 实例：身体质量指数BMI
体质指数（BMI）= 体重（kg）÷ 身高²（m）
代码实例：
height,weight = eval(input("请输入身体(米)和体重(公斤)[逗号分开]："))
bmi = weight / pow(height,2)
print("BMI数值为：{:.2f}".format(bmi))#.2f#保留两位小数
who,nat = "",""
if bmi < 18.5:
who,nat = "偏瘦","偏瘦"
elif 18.5 <= bmi < 24:
who,nat = "正常","正常"
elif 24 <= bmi < 25:
who,nat = "正常","偏胖"
elif 25 <= bmi < 28:
who,nat = "偏胖","偏胖"
elif 28 <= bmi <30:
who,nat = "偏胖","肥胖"
else:
who,nat = "肥胖","肥胖"
print("BMI指标为：国际'{}',国内'{}'".format(who,nat))结果展示：
4 函数和代码复用
4.1 函数的定义和作用
def 函数名(o个或多个参数):
函数体
return 返回值
-函数是一段代码的表示
-函数是一段具有特定功能的、可重用的语句组
-函数是一种功能的抽象，一般函数表达特定功能
两个作用：降低编程难度和代码重用
函数的调用
4.2 函数的参数传递
可选参数传递
函数定义时可以为某些参数定义默认值，构成可选参数。
def test(n,m=1): #m为可选参数
s = 1
for i in range(1,n+1):
s *= i
print(s//m)
test(10)
test(10,2)结果：
可变参数传递
def test(n,*args):#args为可变参数，也可以命名其他值
s = 1
for i in range(1,n+1):
s += i
for item in args:
s += item
print(s)
test(10,3)
test(10,3,1,5)函数执行结果：
参数组合：*args和**kwargs
def test(*args,**kwargs):
print("args =",args)
print("kwargs =",kwargs)
print("----------------------------------")
if __name__ == '__main__':
test(1,5,94,564)
test(a=1,b=2,c=3)
test(1,2,3,4,a=1,b=2,c=3)
test('I love python',1,None,a=1,b=2,c=3)函数执行结果：
参数传递的两种方式：位置传递和名称传递
小结：
函数可以有参数也可以没有，但必须保持括号。*args是可变参数，args接收的是一个tuple；**kw是关键字参数，kw接收的是一个dict。在同时使用*args和**kwargs时，必须*args参数列要在**kwargs前面。
4.3 lambda函数
lambda函数是一种匿名函数，即没有名字的函数；lambda函数用于定义简单的、能够在一行内表示的函数。
g = lambda x,y:x*y
print(g(4,5))6 文件和数据格式化
5.1 文件的使用
Python open() 方法用于打开一个文件，并返回文件对象，在对文件进行处理过程都需要使用到这个函数，如果该文件无法被打开，会抛出 OSError。
常用语法格式
变量名 = open（文件路径（相对或绝对路径），打开模式，encoding=None）
打开模式
| 打开的文件模式 | 描述 |
| ‘r’ | 只读模式，默认值，文件不存在返回FileNotFoundError |
| ‘w’ | 覆盖写模式，文件不存在则创建，存在则完全覆盖 |
| ‘x’ | 创建写模式，文件不存在则创建，存在则返回FileExistsError |
| ‘a’ | 追加写模式，文件不存在则创建，存在则在文件最后追加内容 |
| ‘b’ | 二进制文件模式 |
| ‘t’ | 文本文件模式，默认值 |
| '+' | 与r/w/x/a一同使用，在原功能基础上增加同时读写功能 |
file对象
file 对象使用 open 函数来创建，下表列出了 file 对象常用的函数
| file对象 | 描述 |
| f.read(size) | 读入全部内容，如果给出参数，读入前size长度 |
| f.readline() | 读取整行，包括 "\n" 字符。 |
| f.readlines(sizeint) | 读取所有行并返回列表，若给定sizeint>0，则是设置一次读多少字节，这是为了减轻读取压力。 |
| f.write(s) | 将字符串或字节流写入文件 |
| f.writelines(lines) | 将元素全为字符串的列表写入文件 |
| f.close() | 关闭文件 |
| f.seed(offset) | 调整当前文件操作指针的位置，0-文件开头；1-文件当前位置；2-文件末尾位置 |
| f.flush() | 刷新文件内部缓冲，数据立刻写入文件 |
5.2 wordcloud库的使用
词云以词语为基本单位，更加直观和艺术第展示文件。
wordcloud库官网：https://amueller.github.io/word_cloud/
github地址：https://github.com/amueller/word_cloud
wordcloud下载安装
pip install wordcloudwordcloud常规方法
w = wordcloud.WordCloud()
| 方法 | 描述 | 例子 |
| w.generate(text) | 向wordcloud对象w加载文本text | |
| w.to_file(filename) | 将词云输出.png或.jpg图像文件 | |
实例
import wordcloud
w = wordcloud.WordCloud() #设置wordcloud对象
w.generate("Python by WordCloud,is fun and powerful!") #配置对象参数并加载词云文本
w.to_file("outfile.png") #输出词云文件执行生成图片：
程序执行过程报错：ModuleNotFoundError: No module named 'matplotlib'
解决报错：安装python画图工具第三方库matplotlib：pip install matplotlib
wordcloud工作流程
-
-
- 分割：以空格分割单词
- 统计：单词出现次数并过滤
- 字体：根据统计配置字号
- 布局：颜色环境尺寸
-
配置对象参数
w.wordcloud.WordCloud(<参数>)
| 参数 | 描述 | 例子 |
| width | 指定生成图片宽度，默认400像素 | |
| height | 指定生成图片高度，默认200像素 | |
| min_font_size | 指定词云字体最小字号，默认4号 | |
| max_font_size | 指定词云字体最大字号，根据高度自动调节 | |
| font_step | 指定词云单词步进间隔，默认1 | |
| font_path | 指定文件字体的路径，默认None | font_path="msyh.ttc" |
| max_words | 指定词云显示最多单词数量，默认200 | |
| stopwords | 指定词云排除列表，即不显示的单词列表 | stopwords={"python"} |
| mask | 指定词云形状，默认长方形，修改需应用imread函数 | from scripy.misc import imread mk=imread("pic.png") mask=mk |
| background_color | 指定词云图片背景颜色，默认黑色 | |
实例1
import wordcloud
w = wordcloud.WordCloud()
text = "life is short, you need python"
w = wordcloud.WordCloud(background_color="white",width=500,height=300,
min_font_size=20,max_font_size=40,font_step=6,
max_words=5)
w.generate(text)
w.to_file("outfile2.png")
实例2
import wordcloud
import jieba
text = """
wordcloud是python非常优秀的第三方库，词云以词语为基本单位更加直观和艺术的展示文本词云图，\
也叫文字云，是对文本中出现频率较高的关键词予以视觉化的展现，词云图过滤掉大量的低频低质的文本信息，\
使得浏览者只要一眼扫过文本就可领略文本的主旨。基于Python的词云生成类库,好用功能强大。\
在做统计分析的时候有着很好的应用。
"""
w = wordcloud.WordCloud(width=800,height=400,font_path="msyh.ttc")
w.generate(" ".join(jieba.lcut(text))) #中文需要先分词并组成空格分隔字符串
w.to_file("outfile3.png")
实例3
常规图词云
https://python123.io/resources/pye/新时代中国特色社会主义.txt
import wordcloud
import jieba
f = open("新时代中国特色社会主义","r",encoding="utf-8")
text = jieba.lcut(f.read())
text = " ".join(text)
f.close()
w = wordcloud.WordCloud(background_color='white',width=800,height=400,font_path="msyh.ttc")
w.generate(text)
w.to_file("outfile4.png")实例4
不常规图词云：生成下图五角星形状
import wordcloud
import jieba
from scipy.misc import imread
#图片必须是白色背景色
mask = imread('five-pointed star.png')
f = open("新时代中国特色社会主义","r",encoding="utf-8")
text = jieba.lcut(f.read())
text = " ".join(text)
f.close()
w = wordcloud.WordCloud(background_color='white',width=1000,height=700,font_path="msyh.ttc",mask=mask)
w.generate(text)
w.to_file("outfile5.png")效果
