Python random function

问题:

I'm having problems with Python's import random function. It seems that import random and from random import random are importing different things. I am currently using Python 2.7.3

Python 2.7.3 (default, Apr 10 2012, 23:31:26) [MSC v.1500 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> random()

Traceback (most recent call last):
File "<pyshell#0>", line 1, in <module>
    random()
NameError: name 'random' is not defined
>>> random.randint(1,5)

Traceback (most recent call last):
File "<pyshell#1>", line 1, in <module>
random.randint(1,5)
NameError: name 'random' is not defined
>>> import random
>>> random()

Traceback (most recent call last):
File "<pyshell#3>", line 1, in <module>
random()

TypeError: 'module' object is not callable
>>> random.randint(1,5)
2
>>> from random import random
>>> random()
0.28242411635200193
>>> random.randint(1,5)

Traceback (most recent call last):
File "<pyshell#7>", line 1, in <module>
random.randint(1,5)
AttributeError: 'builtin_function_or_method' object has no attribute 'randint'
>>> 

回答1:

import random imports the random module, which contains a variety of things to do with random number generation. Among these is the random() function, which generates random numbers between 0 and 1.

Doing the import this way this requires you to use the syntax random.random().

The random function can also be imported from the module separately:

from random import random

This allows you to then just call random() directly.

回答2:

The random module contains a function named random(), so you need to be aware of whether you have imported the module into your namespace, or imported functions from the module.

import random will import the random module whereas from random import random will specifically import the random function from the module.

So you will be able to do one of the following:

import random
a = random.random()
b = random.randint(1, 5)
# you can call any function from the random module using random.<function>

or...

from random import random, randint   # add any other functions you need here
a = random()
b = randint(1, 5)
# those function names from the import statement are added to your namespace

回答3:

The problem is that there are two things called random here: one is the module itself, and one is a function within that module. You can't have two things with the same name in your namespace so you have to pick one or the other.

回答4:

import random 

includes the module into the namespace under the name 'random'.

from random import random

includes the function'random' from the namespace 'random' into the global namespace.

So in the first example, you would call random.random, and in the second, you would call random. Both would access the same function.

Similarly,

from random import randint

would import randint into the global namespace, so you could simply call randint instead of random.randint.

回答5:

Well, yes, they import different things. import random imports the random module, from random import random imports the random function from the random module. This is actually a good example of why when designing an API in Python, it's often a good idea to try to avoid naming modules and their members the same thing.

回答6:

The 'random' module is a package from the python standard library, as well as a function defined in this package.

Using 'import random' imports the package, which you can then use the function from this package: 'random.random()'. You can use any other function from the 'random' package as well.

You can also tell python to specifically import only the random function from the package random: 'from random import random'. Then you can only use the function 'random()', and should not specify the package it comes from. However you cannot use any other function from the random package, because they have not been imported if you use 'from random import random'.

回答7:

If you use from random import random, you must call randint() like so: randint(1,5). If you use import random, you call it like so: random.randint(1,5).

回答8:

If you are using PyDev or other clever IDE, make sure it did not import the module automatically, overriding your import. It can be especially confusing here, when module name is equal to a function name, because the error thrown is not a NameError. In my case I added

import random

and later used it:

r = random.radom()

but got:

AttributeError: 'builtin_function_or_method' object has no attribute 'random'

Only after searching I found that PyDev automatically added the line

from random import random

to the end of my imports, so I was in fact calling attribute random of method random. Solution is to delete the automatic import or use it and call the random() method directly.

回答9:

You have to import the random function, from the random module before you can use it use it

In [1]: from random import random

In [2]: random()
Out[2]: 0.5607917948041573