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Ten common Python interview questions

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Release： 2020-09-03 15:30:23

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Ten common Python interview questions

Python is a very popular programming language. With the development of machine learning, cloud computing and other technologies in recent years, the demand for Python positions has become more and more popular. Come higher and higher. Below is a collection of 10 questions frequently asked by Python interviewers for your reference.

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1. Class inheritance

## has the following code:

class A(object):  def show(self):  print 'base show'   class B(A):  def show(self):  print 'derived show'  obj = B()  obj.show()

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How to call class A show method.

The method is as follows:

obj.__class__ = Aobj.show()

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__class__ method points to the class object, just assign it type A, and then call the method show, but Remember to modify it when you are done using it.

2. Method object

Question: In order to make the following code run, what code needs to be added?

class A(object): def __init__(self,a,b): self.__a = a self.__b = b def myprint(self): print 'a=', self.__a, 'b=', self.__b a1=A(10,20) a1.myprint() a1(80)

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Answer: In order to allow the object instance to be called directly, you need to implement the __call__ method

class A(object): def __init__(self, a, b): self.__a = a self.__b = b def myprint(self): print 'a=', self.__a, 'b=', self.__b def __call__(self, num): print 'call:', num + self.__a

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3, new and init

What does the following code output?

class B(object):  def fn(self):  print 'B fn'  def __init__(self):  print "B INIT"  class A(object):  def fn(self):  print 'A fn'  def __new__(cls,a):  print "NEW", a  if a>10:  return super(A, cls).__new__(cls)  return B()  def __init__(self,a):  print "INIT", a  a1 = A(5)  a1.fn()  a2=A(20)  a2.fn()

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Answer:

NEW 5 B INIT B fn NEW 20 INIT 20 A fn

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Using the __new__ method, you can decide which object to return, that is, before creating the object, this can be used Singleton and factory patterns of design patterns. __init__ is called when creating an object.

4. Python list and dict generation

##What does the following code output?

ls = [1,2,3,4]  list1 = [i for i in ls if i>2]  print list1  list2 = [i*2 for i in ls if i>2]  print list2  dic1 = {x: x**2 for x in (2, 4, 6)}  print dic1  dic2 = {x: 'item' + str(x**2) for x in (2, 4, 6)}  print dic2  set1 = {x for x in 'hello world' if x not in 'low level'}  print set1

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Answer:

[3, 4]   [6, 8] {2: 4, 4: 16, 6: 36} {2: 'item4', 4: 'item16', 6: 'item36'} set(['h', 'r', 'd'])

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5. Global and local variables

下面这段代码输出什么?

num = 9   def f1():  num = 20  def f2():  print num  f2()  f1()  f2()

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答案：

9  9

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num不是个全局变量，所以每个函数都得到了自己的num拷贝，如果你想修改num，则必须用global关键字声明。比如下面这样

num = 9  def f1():      global num      num = 20  def f2():     print num  f2()  f1()  f2()  # prints:  #      9  #      20

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6、交换两个变量的值

一行代码交换两个变量值

a=8  b=9

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答案：

(a,b) = (b,a)

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7、默认方法

如下的代码

class A(object):  def __init__(self,a,b):  self.a1 = a  self.b1 = b  print 'init'  def mydefault(self):  print 'default'  a1 = A(10,20)  a1.fn1()  a1.fn2()  a1.fn3()

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方法 fn1/fn2/fn3 都没有定义，添加代码，是没有定义的方法都调用mydefault函数，上面的代码应该输出

defaultdefaultdefault

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答案：

class A(object): def __init__(self,a,b):  self.a1 = a  self.b1 = b  print 'init'  def mydefault(self):  print 'default'  def __getattr__(self,name):  return self.mydefault  a1 = A(10,20)  a1.fn1()  a1.fn2()  a1.fn3()

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方法__getattr__只有当没有定义的方法调用时，才是调用他。当fn1方法传入参数时，我们可以给mydefault方法增加一个*args不定参数来兼容。

class A(object):  def __init__(self,a,b):  self.a1 = a  self.b1 = b  print 'init'  def mydefault(self,*args):  print 'default:' + str(args[0])  def __getattr__(self,name):  print "other fn:",name  return self.mydefault a1 = A(10,20)  a1.fn1(33)  a1.fn2('hello')  a1.fn3(10)

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8、包管理

一个包里有三个模块，mod1.py, mod2.py, mod3.py，但使用from demopack import *导入模块时，如何保证只有mod1、mod3被导入了。

答案:增加__init__.py文件，并在文件中增加：

__all__ = ['mod1','mod3']

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9、闭包

写一个函数，接收整数参数n，返回一个函数，函数的功能是把函数的参数和n相乘并把结果返回。

答案：

def mulby(num):  def gn(val):  return num * val  return gn  zw = mulby(7)  print(zw(9));

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10、性能

解析下面的代码慢在哪

def strtest1(num):  str='first'  for i in range(num):  str+="X"  return str

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答案：python的str是个不可变对象，每次迭代，都会生成新的str对象来存储新的字符串，num越大，创建的str对象越多，内存消耗越大。

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