[Python Learning] Input and Output

foreword

[Python Learning] Lists and Tuples

[Python Learning] Dictionaries and Collections

[Python Learning] Conditions and Loops

In many cases, you will want your program to interact with the user (possibly yourself). You'll get input from the user, and print some results. We can use iinput and print statements to accomplish these functions.

input

name = input('your name:')
gender = input('you are a boy?(y/n)')

###### 输入 ######
your name:Jack
you are a boy?

welcome_str = 'Welcome to the matrix {prefix} {name}.'
welcome_dic = {
    
    
    'prefix': 'Mr.' if gender == 'y' else 'Mrs',
    'name': name
}

print('authorizing...')
print(welcome_str.format(**welcome_dic))

########## 输出 ##########
authorizing...
Welcome to the matrix Mr. Jack.

The input function pauses and waits for keyboard input until the Enter key is pressed. The type of input is always a string

a = input()
1
b = input()
2

print('a + b = {}'.format(a + b))
########## 输出 ##############
a + b = 12
print('type of a is {}, type of b is {}'.format(type(a), type(b)))
########## 输出 ##############
type of a is <class 'str'>, type of b is <class 'str'>
print('a + b = {}'.format(int(a) + int(b)))
########## 输出 ##############
a + b = 3

file input and output

Production-grade Python code with most I/O coming from files

Here is an in.text

Mr. Johnson had never been up in an aerophane before and he had read a lot about air accidents, so one day when a friend offered to take him for a ride in his own small phane, Mr. Johnson was very worried about accepting. Finally, however, his friend persuaded him that it was very safe, and Mr. Johnson boarded the plane.

His friend started the engine and began to taxi onto the runway of the airport. Mr. Johnson had heard that the most dangerous part of a flight were the take-off and the landing, so he was extremely frightened and closed his eyes.

After a minute or two he opened them again, looked out of the window of the plane, and said to his friend。

"Look at those people down there. They look as small as ants, don't they?"

"Those are ants," answered his friend. "We're still on the ground."

Now

read file
Remove all punctuation and line breaks, change uppercase to lowercase
Merge the same words, count the frequency of each word, and sort the word frequency from large to small
Output the result to the file out.txt line by line

import re

# 你不用太关心这个函数
def parse(text):
    # 使用正则表达式去除标点符号和换行符
    text = re.sub(r'[^\w ]', '', text)

    # 转为小写
    text = text.lower()
    
    # 生成所有单词的列表
    word_list = text.split(' ')
    
    # 去除空白单词
    word_list = filter(None, word_list)
    
    # 生成单词和词频的字典
    word_cnt = {
    
    }
    for word in word_list:
        if word not in word_cnt:
            word_cnt[word] = 0
        word_cnt[word] += 1
    
    # 按照词频排序
    sorted_word_cnt = sorted(word_cnt.items(), key=lambda kv: kv[1], reverse=True)
    
    return sorted_word_cnt

with open('in.txt', 'r') as fin:
    text = fin.read()

word_and_freq = parse(text)

with open('out.txt', 'w') as fout:
    for word, freq in word_and_freq:
        fout.write('{} {}\n'.format(word, freq))

########## 输出 (省略较长的中间结果) ##########

But there is a problem, if the file is very large, it is easy to cause memory crash

At this time, specify the parameter size for read. You can also use the readline() function to read one line at a time.

json file read

import json

params = {
    
    
    'symbol': '123456',
    'type': 'limit',
    'price': 123.4,
    'amount': 23
}

params_str = json.dumps(params)

print('after json serialization')
print('type of params_str = {}, params_str = {}'.format(type(params_str), params))

original_params = json.loads(params_str)

print('after json deserialization')
print('type of original_params = {}, original_params = {}'.format(type(original_params), original_params))

########## 输出 ##########

after json serialization
type of params_str = <class 'str'>, params_str = {
    
    'symbol': '123456', 'type': 'limit', 'price': 123.4, 'amount': 23}
after json deserialization
type of original_params = <class 'dict'>, original_params = {
    
    'symbol': '123456', 'type': 'limit', 'price': 123.4, 'amount': 23}

json.dumps() This function accepts Python's basic data type dictionary, and then converts string (json string)

json.loads() This function accepts a legal string (json) and converts it into a dictionary

json reading

import json

params = {
    
    
    'symbol': '123456',
    'type': 'limit',
    'price': 123.4,
    'amount': 23
}

with open('params.json', 'w') as fout:
    params_str = json.dump(params, fout)

with open('params.json', 'r') as fin:
    original_params = json.load(fin)

print('after json deserialization')
print('type of original_params = {}, original_params = {}'.format(type(original_params), original_params))

########## 输出 ##########

after json deserialization
type of original_params = <class 'dict'>, original_params = {
    
    'symbol': '123456', 'type': 'limit', 'price': 123.4, 'amount': 23}