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pythonsyntaxnumeric
JohnGalt
JohnGalt

Reputation: 429

Python syntax - what do two less-signs and one equal sign mean

I've searched for an example to convert WINAPI FILETIME values into UNIX time_t (for a new Golang project) and found an example in Python.

Although I coded many in Python in the past I do not know the <<= and |= syntax in that example and Googles is not able to produce usable results for these search statements.

Could someone explain to me what they do? 

import datetime

_FILETIME_null_date = datetime.datetime(1601, 1, 1, 0, 0, 0)
def FiletimeToDateTime(ft):
    timestamp = ft.dwHighDateTime
    timestamp <<= 32
    timestamp |= ft.dwLowDateTime
    return _FILETIME_null_date + datetime.timedelta(microseconds=timestamp/10)

Upvotes: 1

Views: 56

Answers (2)

aghast
aghast

Reputation: 15310

This is taken from C. It is the '<<' or '|' operator (bitwise shift left and bitwise or, respectively) plus the assignment operator:

a <<= b

Is the same as

a = a << b

Similarly for |=.

Upvotes: 3

Alex Hall
Alex Hall

Reputation: 36043

They are the augmented assignment versions of the bit shift operator << and the bitwise or |, just like += is the augmented +, so:

timestamp <<= 32

is the equivalent of

timestamp = timestamp << 32

Upvotes: 2

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