1. print Function
The arguments of the print function are the following ones:
print(value1, ..., sep=' ', end='\n', file=sys.stdout, flush=False)
The print function can print an arbitrary number of values ("value1, value2, ..."), which are separated by commas. These values are separated by blanks.
2. The built-in function range(a, b) is the right function to iterate over a sequence of numbers;
it includes a but not b in boundary.
3. string -> list:
split(str="", num=string.count(str))
splitlines( num=string.count('\n'))
Splits string at all (or num) NEWLINEs and returns a list of each line with NEWLINEs removed.
4. tuple(seq)
Converts a list into tuple.
5. list(seq)
Converts a sequence into list.
6. set()： sets are lists of strings without duplicated words. set() is used to remove the duplicated elements in a list of string elements;
*** if used in formatting list_string.set(), error below will occur:
AttributeError: 'list' object has no attribute 'set'
the correct way should be: set(list_string);
