Python Note 1

An explanatory object-oriented language.

Strong type. Although it is declared for changes, once a variable has a value, it also has a type. To assign other values, you must use type conversion.

All objects, classes, functions, and modules are objects.

No Boolean, none, 0, "", [], {}, () are false.

List (list, defined as []), which is equivalent to a vector in C ++ or an array in C. Its subscript starts with 0, and negative numbers can be used.

A string consisting of single or double quotation marks. A long string can be defined together with three consecutive double quotes, exceeding multiple rows. The string can be considered as a list of many characters.

Tuple is a constant list, represented by (). The brackets are omitted. The tuples can return elements or sub-tuple by subscript. The tuples can be used to assign values to multiple variables, such as, B = (1, 2 ).

Sequence includes string, list, And tuple. They have some common operations: Using in to determine whether an element is in the sequence: If X in
Seq. Obtain the length of the sequence Len (SEQ ). Use subscript to retrieve element SQL [I] And subseq: SQL [start: end] By subscript with colon, and use + to connect
Input two seq, and use * to represent repeated seq.

A dictionary is an unordered structure. Each element is a pair, including value and key. The key type is integer or
The string and value types are arbitrary. The dictionary does not contain duplicate keys. Each element in the dictionary is a tuple, which includes
Elements, keys, and values are called pair. In pair, values are followed by keys. You can use d [Key] to obtain the value. The dictionary is enclosed.

Conditional statement if:

If <expr1 >:< one-line-Statement>

Or

if <expr1>:
    <statement-block>

Or

    if <expr1>:
    <statement-block>
    else:
    <statement-block>

Or

    if <expr1>:
    <statement-block>
    elif <expr2>:
    <statement-block>
    elif <expr3>:
    <statement-block>
    ...
    else:
    <statement-block>