What is the logic of python * syntax when iterating over a tuple sequence?

The

code is taken from page 4 of the third edition of pythoncookbook. The code is as follows: 

records =[
    ("foo", 1, 2),
    ("batr", "hello"),
    ("foo", 3 ,4),
]
def do_foo(x,y):
    print("foo", x ,y)

def do_bar(s):
    print("bar", s)

for tag, *args in records:
    if tag == "foo":
        do_foo(*args)
    elif tag == "bar":
        do_bar(*args)
:
foo 1 2
foo 3 4

the principle of the code is not very clear. Please explain it. Thank you.

Python
Mar.21,2021

I guess your confusion may be why the: bar hello results didn't show up?
because the second item of your records is misspelled: ('batr',' hello') should be ('bar',' hello'), 

In [1]: records =[
   ...:     ('foo', 1, 2),
   ...:     ('bar', 'hello'),
   ...:     ('foo', 3 ,4),
   ...: ]
   ...: def do_foo(x,y):
   ...:     print('foo', x ,y)
   ...: 
   ...: def do_bar(s):
   ...:     print('bar', s)
   ...: 
   ...: for tag, *args in records:
   ...:     if tag == 'foo':
   ...:         do_foo(*args)
   ...:     elif tag == 'bar':
   ...:         do_bar(*args)
   ...:         
foo 1 2
bar hello
foo 3 4

the simple explanation is:
* arg decomposes several elements after tag.
for example, the three elements in the list record are: ('foo', 1 hello' 2) (' bar', 'hello') (' foo', 3, 4)
tag is' element after foo', (1 br 2) is * args, so print foo 1 2
tag as' element behind bar', 'hello' is * args, So print bar hello
tag as' foo', followed by the element (3) is * args, so print foo 3 4

< H2 > use * to process the remaining elements < / H2 >

-- page 25 of "smooth python"

in Python, it is a classic way for a function to use * args to get an uncertain number of parameters.
in Python 3, this concept extends to parallel assignments: 

>>> a, *body, c, d = range(5)
>>> a, body, c, d
(0, [1, 2], 3, 4]
>>> *head, b, c, d = range(5)
([0, 1], 2, 3, 4]

Previous: Chrome and firefox header th width value problem?

Next: A problem of query Optimization

css mysql arrays josn react html typescript webpack npm sass R objective-c .net sql-server jquery python-3.x angularjs django angular excel regex iphone ajax linux xml pandas vba spring database wordpress string wpf xcode windows bash postgresql oracle multithreading eclipse list firebase algorithm macos forms image scala visual-studio azure bootstrap spring-boot react-native python-2.7 docker performance function winforms matlab powershell apache dataframe api sqlite numpy rest shell selenium flutter dart maven loops qt swing android-studio csv express file class tensorflow sorting codeigniter perl
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1e34075-4429c.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1e34075-4429c.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
Need Help?