What are >> and << for?
I read this in code:
https://github.com/mlaiosa/emlx2maildir/blob/master/emlx2maildir.py
FL_READ = (1<<0)
FL_DELETED = (1<<1)
FL_ANSWERED = (1<<2)
FL_ENCRYPTED = (1<<3)
FL_FLAGGED = (1<<4)
FL_RECENT = (1<<5)
FL_DRAFT = (1<<6)
FL_INITIAL = (1<<7)
FL_FORWARDED = (1<<8)
FL_REDIRECTED = (1<<9)
FL_SIGNED = (1<<23)
FL_IS_JUNK = (1<<24)
FL_IS_NOT_JUNK = (1<<25)
FL_JUNK_LEVEL_RECORDED = (1<<29)
FL_HIGHLIGHT_IN_TOC = (1<<30)
I cannot find the documentation of it yet.
It's bitshift operator. If you have a 1(0b1), and shift it left 4 bits(1 << 4), what you get is 0b10000, which means 16.
And here's the documentation: http://docs.python.org/reference/expressions.html#shifting-operations
1, then you assign second flag 1 << 1, third flag 1 << 2 etc. And when checking this flags, and when you checking for a flag you use flag & flag_name, if it yields 1, you have the flag, 0, you don't.
The operators are defined in section 5.7, "Shifting Operations", of the Python Language Reference:
These operators accept plain or long integers as arguments. The arguments are converted to a common type. They shift the first argument to the left or right by the number of bits given by the second argument.
A right shift by n bits is defined as division by
pow(2, n). A left shift by n bits is defined as multiplication withpow(2, n). Negative shift counts raise aValueErrorexception.
In most languages, including Python, those are shift-operators. They work on the bits of a byte.
For example, 8 is 0b00001000. 8 >> 1 means shift the bits of it 1 digit to the right, adding a zero at the left (0b00000100 or 4). 8 >> 2 means shift it to the right twice. (0b00000010 or 2). The << is a left shift, which works in the opposite way. 8 << 1 would come out to 0b00010000 or 16. 8 << 2 would come out to 0b00100000 or 32.
See the python documentation for more information.
Python 2.x: http://docs.python.org/reference/expressions.html#shifting-operations
Python 3.x: http://docs.python.org/py3k/reference/expressions.html#shifting-operations
