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We can simply use:
crc = struct.unpack('>i', data)
why do people write it like this:
(crc,) = struct.unpack('>i', data)
What does the comma mean?
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A comma forms a tuple, which in Python looks just like an immutable list. Python does destructuring assignment, found in a few other languages, e.g. modern JavaScript. In short, a single assignment can map several left-hand variables to the same number of right-hand values: foo, bar = 1, 2.
Unpacking in Python refers to an operation that consists of assigning an iterable of values to a tuple (or list ) of variables in a single assignment statement. As a complement, the term packing can be used when we collect several values in a single variable using the iterable unpacking operator, * .
Unpacking in Python refers to assigning values in an iterable object to a tuple or list of variables for later use. We can perform unpacking by using an asterisk ( * ) before the object we would like to unpack.
Summary. Unpacking assigns elements of the list to multiple variables. Use the asterisk (*) in front of a variable like this *variable_name to pack the leftover elements of a list into another list.
The first variant returns a single-element tuple:
In [13]: crc = struct.unpack('>i', '0000')
In [14]: crc
Out[14]: (808464432,)
To get to the value, you have to write crc[0].
The second variant unpacks the tuple, enabling you to write crc instead of crc[0]:
In [15]: (crc,) = struct.unpack('>i', '0000')
In [16]: crc
Out[16]: 808464432
the unpack method returns a tuple of values. With the syntax you describe one can directly load the first value of the tuple into the variable crc while the first example has a reference to the whole tuple and you would have to access the first value by writing crc[1] later in the script.
So basically if you only want to use one of the return values you can use this method to directly load it in one variable.
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