some interview question

The combined dictionary: merge the two dictionaries below a = { "A": 1, "B": 2}, b = { "C": 3, "D": 4}

dict1 = {"A": 1, "B": 2}
dict2 = {"C": 3, "D": 4}

# 方式一  **表示打散
print({**dict1, **dict2})  # *   ** 都表示打散可迭代对象

# 方式二 update方法
dict1.update(dict2)   # 合并字典

Tuple Operation: How tuples ( "a", "b") and the tuple (1,2), the dictionary becomes { "a": 1, "b": 2}
```
# zip的使用
a = ("a", "b")
b = (1, 2)
print(dict(zip(a, b)))
```

Exchange dictionary of keys and values

dict1 = {"A": 1, "B": 2}
res = {k: v for v, k in dict1.items()}
print(res)

We know that the list can be selected using the slicing of some elements, then how to achieve the same functionality of the object generator type it?
Python exchange two variables
```
a,b=b,a
```
This is not a tuple unpacked, in exchange of two values at the top of the stack.

read()/readline()/readlines()

with open('test.txt', 'r', encoding='utf-8') as f:
    text = f.read()
    print(text)

with open('test.txt', 'r', encoding='utf-8') as f:
    try:
        line = f.readline()
        if line:
            print(line)
    except:
        pass

with open('test.txt', 'r', encoding='utf-8') as f:
    try:
        lines = f.readlines()  # 全部加载到内存
        for line in lines:
            print(line)
    except:
        pass

json serialization, data types can be supported is str / int / tuple / dict / bool / None, but does not support datetime json serialization.

json serialization encountered Chinese converted to Unicode, you want to keep the Chinese how to do?

import json

a = json.dumps({"name": "张三"})
print(a)
"""
{"name": "\u5f20\u4e09"}
"""

import json

a = json.dumps({"name": "张三"}, ensure_ascii=False)
print(a)
"""
{"name": "张三"}
"""

AB two documents which are letters, read out after a good sort, written in C file inside

with open('test1.txt', 'r') as f1:
    line1 = f1.readline()
with open('test2.txt', 'r') as f2:
    line2 = f2.readline()
line = line1 + line2
line = sorted(line)
print(line)
with open("test3.txt", "a+") as f:
    f.write("".join(line))

Seek plus N days based on the current time on the date

import datetime
def datetime_operate(num:int):
    now = datetime.datetime.now()
    _new_date=now+datetime.timedelta(days=num)
    # 再将这个数字转换为标准的时间
    new_date = _new_date.strftime("%Y%m%d")
    return new_date
if __name__=="__main__":
    res = datetime_operate(10)
    print(res)

What is wrong with the following code
```
def strappend(num)：
    str='first'
    for i in range(num)：
        str+=str(i)
    return str
```
Questions are as follows:
1. str is a built-in function, should not be used as variable names.
2. str is an immutable object, each iteration will occupy the new space, the greater the num, the greater the wasted space into a generator to yield.
3. From the naming convention in terms of function, function names, use delimiter better.
```
def str_append(num):
    s = 'first'
    for i in range(num):
        s += str(i)
        yield s

if __name__ == '__main__':
    for i in str_append(3):
        print(i)
```
with the statement of the role, to write a piece of code?

with the statement that the context management protocol, which contains this __enter__and __exit__two methods. statement for the occasion with access to resources, ensuring that regardless of whether an exception occurs during use to perform the necessary cleanup operations, the release of resources, such as files automatically shut down after, thread lock automatically acquired and released.
```
class Test:
    def __enter__(self):
        print('__enter__() is called!')
        return self
    def dosomething(self):
        print('do something!')
    def __exit__(self,*args,**kwargs):
        print('__exit__() is called!')
with Test() as sample:
    sample.dosomething()
```

Statistics document the number of uppercase letters

with open('A.txt') as f:
    count=0
    for word in f.read():
        if word.isupper():
            count+=1
    print(count)

Redis basic types
- string
- hash
- list
- set
- zset (sorted set: an ordered collection)
Python connection MySQL / MongoDB / Redis
Three database paradigm
Distributed Lock
Redis Affairs
Decorator What is the role? for example?

Decorator is a function, without changing any code changes to the premise of a function to add additional functionality, play a decorative effect.

Scenario:

Insert log
Performance Testing
Transaction Processing
Cache

Check permissions

from functools import wraps
def log(label):
    def decorate(func):
        @wraps(func)
        def _wrap(*args,**kwargs):
            try:
                func(*args,**kwargs)
                print("name",func.__name__)
            except Exception as e:
                print(e.args)
            return _wrap
        return decorate
@log("info")
def foo(a,b,c):
    print(a+b+c)
    print("in foo")

if __name__=="__main__":
    foo(1,2,3)
 # mark一下，这个还需要认真琢磨琢磨。

------------------

Python garbage collection

For Python language is concerned, the object type and memory are determined at runtime, which is why we called Python language is dynamically typed reasons.

Garbage collection:
- Application counting mechanism
- Mark - Clear
- Generational recovery

Magic function __call__how to use?

class Bar:
    def __call__(self,*args,**kwargs):
        print("in call")

if __name__=="__main__":
    b=Bar()
    b()

Determine a target is a function or method?

from types import MethodType, FunctionType


class Bar:
    def foo(self):
        pass


def foo1():
    pass


print("foo是函数", isinstance(Bar().foo, FunctionType))
print("foo是方法", isinstance(Bar().foo, MethodType))

The mass participation python is pass by value or address?

Parameter passing in Python is neither value nor the transfer address pass, pass application object.
Python Metaclass (the metaclass that) Example of use.
What is a monkey patch?
Memory Management
Regular Expressions

enumerate

enumerate can be an object in the iteration time, and at the same time to get the current index value of the object

from string import ascii_lowercase
from string import ascii_uppercase
s = ascii_uppercase
for index, value in enumerate(s):
    print(index, value)

It lists five standard modules
- pathlib route operation module
- urllib network requesting module
- asyncio Python asynchronous library
- re a regular expression module
- itertools operation module number generator

Python exception handling

try:
    1 / 0
except Exception as e:
    print(e)
'''
division by zero
'''

The maximum number of recursion in python

A: The maximum number of defaults to 1000, general computer can only reach 998.

import sys
sys.setrecursionlimit(1500)
# 这个只是修改的Python解释器允许的最大递归次数，此外限制还和OS有关。

Object-oriented mro

Call the class object mro () method to get their inheritance.

Affirm:

Python is the assertion statement to achieve this function, the general expression to true, the procedures to be adopted.

# assert() 断言成功，程序继续执行，断言失败，程序报错。
# 断言能够帮助别人活着未来的你理解代码
# 找出程序中逻辑不对的地方
# 一方面，断言会提醒你某个对象应该处于何种状态
# 另一方面 ，如果某个时候断言为假，会抛出异常
def foo(a):
    assert a==2,Exception('不等于2')
    print('ok',a)
if __name__=='__main__':
    foo(1)

lambda expression is an anonymous function is often used as an argument in the function programming.
5 include the exception type as well as its meaning Python
- AttributeError object does not have this property
- Methods NotImplementedError unfulfilled
- StopIteration iterator no more value
- TypeError invalid type of operation
- IndentationError indentation errors
Sort of the difference between listed and sorted:

Similarities sorted can be sorted and sort the list of elements, sort () and sorted () is different from that, sort list is rearranged in situ and sorted () is to generate a new list. The method is applied on the sort of the list, sorted can be sorted objects operate all iterations. list sort method returns a list of the existing operation, the built-in function sorted method returns a new list, rather than operation performed on the basis of the original.

Ary issues

print(int(0b1010))
print(bin(0xf))
print(oct(8))
print(hex(16))
'''
10
0b1111
0o10
0x10
'''

Algorithms and data structures:

Implement a binary function looks with Python

def binary_search(arr, num):
    n = len(arr)
    left = 0
    right = n - 1  # 最右边的index
    while left <= right:
        mid = (left + right) // 2
        if num == arr[mid]:
            return "index:" + str(mid)
        elif num < arr[mid]:
            right = mid - 1  # 比中间的小
        else:
            left = mid + 1  # 比中间的大
    return False  # 从这个循环里面跳出来说明木有找到，返回False


if __name__ == "__main__":
    lst = [1, 3, 4, 5, 7, 100]
    res = binary_search(lst, 7)
    print(res)

some interview question

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