python基础（九）

#文件和异常
'''
处理文件
错误处理
json，保存用户数据
'''

从文件中读取数据

#读取整个文件 
with open('pi_digits.txt') as file_object: 
　　contents = file_object.read() 
　　print(contents)
'''
open接受的参数：要打开文件的名称，在当前所执行的文件所在目录找到指定文件；
函数open()返回一个表示文件的对象，python将这个对象存储在我们将在后面使用的变量中；
使用方法read读取这个文件的全部内容，并将其作为一个长长的字符串存储在变量contents中
'''
with open('pi_digits.txt') as file_object:
    contents = file_object.read()
    print(contents.rstrip())

3.1415926535 
  8979323846 
  2643383279

#文件路径

with open('text_files/pi_digits.txt') as file_object:
    contents = file_object.read()
    print(contents.rstrip())

3.1415926535 
  8979323846 
  2643383279

file_path = 'text_files/pi_digits.txt'
with open(file_path) as file_object:
    contents = file_object.read()
    print(contents.rstrip())

#逐行读取
filename = 'pi_digits.txt'
with open(filename) as file_object:
    for line in file_object:
        print(line)

3.1415926535 

  8979323846 

  2643383279

filename = 'pi_digits.txt'
with open(filename) as file_object:
    for line in file_object:
        print(line.rstrip())

3.1415926535
  8979323846
  2643383279

#创建一个包含文件各行内容的列表
'''
with
open()返回的文件对象只在with代码块内可用
要在代码块外访问文件内容，可以将文件的各行存储在一个列表中
'''

filename = 'pi_digits.txt'
with open(filename) as file_object:
    lines = file_object.readlines()

for line in lines :
    print(line.rstrip())

3.1415926535
  8979323846
  2643383279

#使用文件的内容
filename = 'pi_digits.txt'
with open(filename) as file_object:
    lines = file_object.readlines()
    
pi_string = ''
for line in lines:
    pi_string += line.rstrip()

print(pi_string)
print(len(pi_string))

3.1415926535  8979323846  2643383279
36

#删除空格strip
filename = 'pi_digits.txt'
with open(filename) as file_object:
    lines = file_object.readlines()
    
pi_string = ''
for line in lines:
    pi_string += line.strip()

print(pi_string)
print(len(pi_string))

3.141592653589793238462643383279
32

#包含一百万位的大型文件
filename = 'pi_million_digits.txt'

with open(filename) as file_object:
    lines = file_object.readlines()
    
pi_string = ''
for line in lines:
    pi_string += line.strip()

print(pi_string[:52] + "...")
print(len(pi_string))

3.14159265358979323846264338327950288419716939937510...
1000002

#圆周率中包含你的生日吗
filename = 'pi_million_digits.txt'

with open(filename) as file_object:
    lines = file_object.readlines()
    
pi_string = ''
for line in lines:
    pi_string += line.strip()

birthday = input("Enter your birthday,in the form mmddyy:")
if birthday in pi_string:
    print("Yes! In!")
else:
    print("Sorry.")

Enter your birthday,in the form mmddyy:0201
Yes! In!

写入文件

保存数据的最简单的方式
将输出写入文件，程序输出终端窗口关闭了，输出也存在
查询，分享，输出处理

#写入空文件
filename = 'programming.txt'

with open(filename, 'w') as file_object:
    file_object.write("I love programming.")

'w'以写入模式打开，读取模式'r'，附加模式'a'，读取和写入文件的模式'r+'
如果你要写入的文件不存在，函数open()将自动创建它，'w'以写入模式，如果文件已经存在，将会被覆盖

#写入多行
filename = 'programming.txt'

with open(filename, 'w') as file_object:
    file_object.write("I love programming.")
    file_object.write("I love creating new games.")

#两行挤在一起
filename = 'programming.txt'

with open(filename, 'w') as file_object:
    file_object.write("I love programming.
")
    file_object.write("I love creating new games.
")

#添加到文件
'''
给文件添加新的内容，附加模式
'''
filename = 'programming.txt'

with open(filename, 'a') as file_object:
    file_object.write("I also love finding meaning in large datasets.
")

异常

异常使用trace-except代码块处理
处理ZoreDivisionError

print(5/0)

---------------------------------------------------------------------------
ZeroDivisionError                         Traceback (most recent call last)
<ipython-input-21-cfd0a335a8dd> in <module>
      1 #异常使用trace-except代码块处理
      2 #处理ZoreDivisionError
----> 3 print(5/0)

ZeroDivisionError: division by zero

try:
    print(5/0)
except ZeroDivisionError:
    print("You can't divide by zero.")

You can't divide by zero.

#使用异常避免崩溃
print("Give me two numbers, and I'll divide them.")
print("Enter 'q' to quit.")

while True:
    first_number = input("
First number: ")
    if first_number == 'q':
        break
    second_number = input("Second number: ")
    if second_number == 'q':
        break
    answer = int(first_number) / int(second_number)
    print(answer)

Give me two numbers, and I'll divide them.
Enter 'q' to quit.

First number: 5
Second number: 2
2.5

First number: 5
Second number: 0

---------------------------------------------------------------------------
ZeroDivisionError                         Traceback (most recent call last)
<ipython-input-24-c3edc14c8e87> in <module>
     10     if second_number == 'q':
     11         break
---> 12     answer = int(first_number) / int(second_number)
     13     print(answer)

ZeroDivisionError: division by zero

print("Give me two numbers, and I'll divide them.")
print("Enter 'q' to quit.")

while True:
    first_number = input("
First number: ")
    if first_number == 'q':
        break
    second_number = input("Second number: ")
    try:
        answer = int(first_number) / int(second_number)
    except ZeroDivisionError:
        print("You can't divide by zero.")
    else:
        print(answer)

Give me two numbers, and I'll divide them.
Enter 'q' to quit.

First number: 5
Second number: 0
You can't divide by zero.

First number: q

#处理FileNotFoundError异常
filename = 'alice.txt'

with open(filename) as f_obj:
    contents = f_obj.read()

---------------------------------------------------------------------------
FileNotFoundError                         Traceback (most recent call last)
<ipython-input-26-1609d2652e61> in <module>
      2 filename = 'alice.txt'
      3 
----> 4 with open(filename) as f_obj:
      5     contents = f_obj.read()

FileNotFoundError: [Errno 2] No such file or directory: 'alice.txt

filename = 'alice.txt'

try:
    with open(filename) as f_obj:
        contents = f_obj.read()
except FileNotFoundError:
    msg = "Sorry, the file " + filename + "does not exit."
    print(msg)

Sorry, the file alice.txtdoes not exit.

#分析文本
title = "Alice in WonderIand"
print(title.split())

['Alice', 'in', 'WonderIand']

filename = 'alice.txt'

try:
    with open(filename) as f_obj:
        contents = f_obj.read()
except FileNotFoundError:
    msg = "Sorry, the file " + filename + "does not exit."
    print(msg)

else:
    words = contents.split()
    num_words = len(words)
    print("The file " + filename + " has about " + str(num_words) + " words.")

Sorry, the file alice.txtdoes not exit.

#对变量contents调用方法split()，生成一个列表
#使用多个文件
'''
多分析几本书，将这个程序的大部分代码转移到一个函数中
'''
def count_words(filename):
    try:
        with open(filename) as f_obj:
            contents = f_obj.read()
    except FileNotFoundError:
        msg = "Sorry, the file " + filename + "does not exit."
        print(msg)
    else:
        words = contents.split()
        num_words = len(words)
        print("The file " + filename + " has about " + str(num_words) + " words.")   

filename = 'alice.txt'
count_words()

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-30-3efecb085eee> in <module>
     16 
     17 filename = 'alice.txt'
---> 18 count_words()

TypeError: count_words() missing 1 required positional argument: 'filename'

def count_words(filename):
    try:
        with open(filename) as f_obj:
            contents = f_obj.read()
    except FileNotFoundError:
        msg = "Sorry, the file " + filename + "does not exit."
        print(msg)
    else:
        words = contents.split()
        num_words = len(words)
        print("The file " + filename + " has about " + str(num_words) + " words.")   

filenames = ['alice.txt', 'siddhartha.txt', 'moby_dick.txt', 'little_women.txt']
for filename in filenames:
    count_words(filename)

#失败时一声不吭，
'''
    except FileNotFoundError:
        pass
'''
#决定报告那些错误

line.count('X')

6

line = "XXXXXX"
line.lower().count('x')

6

存储数据

使用模块json，能够将简单的python数据结构转储到文件中，并在程序再次运行的时候加载该文件中的数据。
还可用于分享
使用json.dump() json.load()
编写一个存储一组数字的简短程序，再编写一个将这些数字读取到内存中的程序。

import json

numbers = [2,3,4,7,9]

filename = 'numbers.json'
with open(filename, 'w') as f:
    json.dump(numbers, f)

filename = 'numbers.json'
with open(filename) as f:
    numbers = json.load(f)
    
print(numbers)

[2, 3, 4, 7, 9]

#保存和读取用户生成的数据
username = input("What is your name?")
filename = 'username.json'
with open(filename, 'w') as f:
    json.dump(username, f)
    print("hello, " + username + ".")

What is your name?jing
hello, jing.

filename = 'username.json'
with open(filename) as f:
    username = json.load(f)
    
print(username)

jing

filename = 'username.json'
try:
    with open(filename) as f:
        username = json.load(f)
except FileNotFoundError:
    username = input("What is your name?")
    with open(filename, 'w') as f:
        json.dump(username, f)
        print("hello, " + username + ".")
else:
    print("welcome" + username + ".")

What is your name?jing
hello, jing.

#重构
'''
将代码划分为一系列完成具体工作的函数。
greet_user()所做的不仅仅是问候用户，还在存储了用户名时获取它，而在没有用户名时提示用户输入一个。
'''
import json

def greet_user():
    filename = 'username.json'
    try:
        with open(filename) as f:
            username = json.load(f)
    except FileNotFoundError:
        username = input("What is your name?")
        with open(filename, 'w') as f:
            json.dump(username, f)
            print("hello, " + username + ".")
    else:
        print("welcome" + username + ".")

greet_user()

welcomejing.

'''
get_stored_username()如果存储了用户名，就返回它，如果没有存储就返回None。

'''
import json

def get_stored_username():
    filename = 'username.json'
    try:
        with open(filename) as f:
            username = json.load(f)
    except FileNotFoundError:
        return None
    else:
        return username
    
def greet_user():
    username = get_stored_username()
    if username:
        print("welcome" + username + ".")
    else:
        username = input("What is your name?")
        with open(filename, 'w') as f:
            json.dump(username, f)
            print("hello, " + username + ".")
            
greet_user()

welcomejing.

'''
greet_user()欢迎老客户回来，欢迎新客户
get_stored_username()只负责获取存储的用户名
get_new_username()只负责获取并存储新用户名
'''
import json

def get_stored_username():
    filename = 'username.json'
    try:
        with open(filename) as f:
            username = json.load(f)#获取
    except FileNotFoundError:
        return None
    else:
        return username
    
def get_new_username():
    username = input("What is your name?")
    filename = 'username.json'
    with open(filename, 'w') as f:
        json.dump(username, f)#存储
    return username

def greet_user():
    username = get_stored_username()#老
    if username:
        print("welcome" + username + ".")
    else:
        username = get_new_username()#新
        print("hello, " + username + ".")
    
greet_user()

welcomejing.