Is there a difference between 'and' and &#

问题:

I got very good help for question check if dictionary key has empty value . But I was wondering if there is a difference between and and & in python? I assume that they should be similar?

dict1 ={"city":"","name":"yass","region":"","zipcode":"",
   "phone":"","address":"","tehsil":"", "planet":"mars"}

whitelist = {"name", "phone", "zipcode", "region", "city",
             "munic", "address", "subarea"}

result = {k: dict1[k] for k in dict1.viewkeys() & whitelist if dict1[k]}

回答1:

and is a logical operator which is used to compare two values, IE:

> 2 > 1 and 2 > 3
True

& is a bitwise operator that is used to perform a bitwise AND operation:

> 255 & 1
1

Update

With respect to set operations, the & operator is equivalent to the intersection() operation, and creates a new set with elements common to s and t:

>>> a = set([1, 2, 3])
>>> b = set([3, 4, 5])
>>> a & b
set([3])

and is still just a logical comparison function, and will treat a set argument as a non-false value. It will also return the last value if neither of the arguments is False:

>>> a and b
set([3, 4, 5])
>>> a and b and True
True
>>> False and a and b and True
False

---

For what its worth, note also that according to the python docs for Dictionary view objects, the object returned by dict1.viewkeys() is a view object that is "set-like":

The objects returned by dict.viewkeys(), dict.viewvalues() and dict.viewitems() are view objects. They provide a dynamic view on the dictionary’s entries, which means that when the dictionary changes, the view reflects these changes.

...

dictview & other

Return the intersection of the dictview and the other object as a new set.

...

回答2:

• and is logical and
• & is bitwise and

logical and returns the second value if both values evaluate to true.

For sets & is intersection.

If you do:

In [25]: a = {1, 2, 3}

In [26]: b = {3, 4, 5}

In [27]: a and b
Out[27]: set([3, 4, 5])

In [28]: a & b
Out[28]: set([3])

This be because bool(a) == True and bool(b) == True so and returns the second set. & returns the intersection of the sets.

(set doc)

回答3:

Yes and is a logical and whereas & is a bitwise and. See example -

>>> 1 and 2
2
>>> 1 & 2
0

The first result is due to short circuiting. Python tests 1 and finds it true and returns the 2. But, the second part does 01 (Binary 1) & 10 (Binary 2) hence evaluating to 00 (1 & 0, 0 &1) , which is 0.

回答4:

&is the bit-wise and operator, and is the boolean logic operator. They're quite different, don't confuse them! For example:

7 & 3
=> 3

True and False
=> False

回答5:

>>> help('&')

+-------------------------------------------------+---------------------------------------+
| Operator                                        | Description                           |
+=================================================+=======================================+
| ``lambda``                                      | Lambda expression                     |
+-------------------------------------------------+---------------------------------------+
| ``if`` -- ``else``                              | Conditional expression                |
+-------------------------------------------------+---------------------------------------+
| ``or``                                          | Boolean OR                            |
+-------------------------------------------------+---------------------------------------+
| ``and``                                         | Boolean AND                           |
+-------------------------------------------------+---------------------------------------+
| ``not`` ``x``                                   | Boolean NOT                           |
+-------------------------------------------------+---------------------------------------+
| ``in``, ``not in``, ``is``, ``is not``, ``<``,  | Comparisons, including membership     |
| ``<=``, ``>``, ``>=``, ``<>``, ``!=``, ``==``   | tests and identity tests,             |
+-------------------------------------------------+---------------------------------------+
| ``|``                                           | Bitwise OR                            |
+-------------------------------------------------+---------------------------------------+
| ``^``                                           | Bitwise XOR                           |
+-------------------------------------------------+---------------------------------------+
| ``&``                                           | Bitwise AND                           |
+-------------------------------------------------+---------------------------------------+
| ``<<``, ``>>``                                  | Shifts                                |
+-------------------------------------------------+---------------------------------------+
| ``+``, ``-``                                    | Addition and subtraction              |
+-------------------------------------------------+---------------------------------------+
| ``*``, ``/``, ``//``, ``%``                     | Multiplication, division, remainder   |
|                                                 | [8]                                   |
+-------------------------------------------------+---------------------------------------+
| ``+x``, ``-x``, ``~x``                          | Positive, negative, bitwise NOT       |
+-------------------------------------------------+---------------------------------------+
| ``**``                                          | Exponentiation [9]                    |
+-------------------------------------------------+---------------------------------------+
| ``x[index]``, ``x[index:index]``,               | Subscription, slicing, call,          |
| ``x(arguments...)``, ``x.attribute``            | attribute reference                   |
+-------------------------------------------------+---------------------------------------+
| ``(expressions...)``, ``[expressions...]``,     | Binding or tuple display, list        |
| ``{key: value...}``, ```expressions...```       | display, dictionary display, string   |
|                                                 | conversion                            |
+-------------------------------------------------+---------------------------------------+