问题
I notice that I can do things like 2 << 5 to get 64 and 1000 >> 2 to get 250.
Also I can use >> in print:
print >>obj, "Hello world"
What is happening here?
回答1:
These are bitwise shift operators.
Quoting from the docs:
x << y
Returns x with the bits shifted to the left by y places (and new bits on the right-hand-side are zeros). This is the same as multiplying x by 2**y.
x >> y
Returns x with the bits shifted to the right by y places. This is the same as dividing x by 2**y.
回答2:
I think it is important question and it is not answered yet (the OP seems to already know about shift operators). Let me try to answer, the >> operator in your example is used for two different purposes. In c++ terms this operator is overloaded. In the first example it is used as bitwise operator (left shift), while in the second scenario it is merely used as output redirection. i.e.
2 << 5 # shift to left by 5 bits
2 >> 5 # shift to right by 5 bits
print >> obj, "Hello world" # redirect the output to obj,
example
with open('foo.txt', 'w') as obj:
print >> obj, "Hello world" # hello world now saved in foo.txt
update:
In python 3 it is possible to give the file argument directly as follows:
print("Hello world", file=open("foo.txt", "a")) # hello world now saved in foo.txt
回答3:
The other case involving print >>obj, "Hello World" is the "print chevron" syntax for the print statement in Python 2 (removed in Python 3, replaced by the file argument of the print() function). Instead of writing to standard output, the output is passed to the obj.write() method. A typical example would be file objects having a write() method. See the answer to a more recent question: Double greater-than sign in Python.
回答4:
12 << 2
48
Actual binary value of 12 is "00 1100" when we execute the above statement Left shift ( 2 places shifted left) returns the value 48 its binary value is "11 0000".
48 >> 2
12
The binary value of 48 is "11 0000", after executing above statement Right shift ( 2 places shifted right) returns the value 12 its binary value is "00 1100".
回答5:
These are the shift operators
x << y Returns x with the bits shifted to the left by y places (and new bits on the right-hand-side are zeros). This is the same as multiplying x by 2**y.
x >> y Returns x with the bits shifted to the right by y places. This is the same as //'ing x by 2**y.
回答6:
They are bit shift operator which exists in many mainstream programming languages, << is the left shift and >> is the right shift, they can be demonstrated as the following table, assume an integer only take 1 byte in memory.
| operate | bit value | octal value | description |
| ------- | --------- | ----------- | -------------------------------------------------------- |
| | 00000100 | 4 | |
| 4 << 2 | 00010000 | 16 | move all bits to left 2 bits, filled with 0 at the right |
| 16 >> 2 | 00000100 | 4 | move all bits to right 2 bits, filled with 0 at the left |
来源：https://stackoverflow.com/questions/22832615/what-do-and-mean-in-python