Interpreter Design Pattern
Videos
| Section | Video Links |
|---|---|
| Interpreter Overview |    |
| Interpreter Use Case | |
| String Slicing | |
| repr Dunder Method | |
Book
Overview
... Refer to Book, pause Video Lectures or subscribe to Medium Membership to read textual content.
Terminology
... Refer to Book, pause Video Lectures or subscribe to Medium Membership to read textual content.
Interpreter UML Diagram
Source Code
... Refer to Book, pause Video Lectures or subscribe to Medium Membership to read textual content.
Output
python ./interpreter/interpreter_concept.py 5 + 4 - 3 + 7 - 2 ['5', '+', '4', '-', '3', '+', '7', '-', '2'] 11 ((((5 Add 4) Subtract 3) Add 7) Subtract 2)
Example Use Case
... Refer to Book, pause Video Lectures or subscribe to Medium Membership to read textual content.
Example UML Diagram
Output
python ./interpreter/client.py 5 + IV - 3 + VII - 2 ['5', '+', 'IV', '-', '3', '+', 'VII', '-', '2'] 11 ((((5 Add IV(4)) Subtract 3) Add VII(7)) Subtract 2)
New Coding Concepts
String Slicing
Sometimes you want part of a string. In the example code, when I am interpreting the roman numerals, I am comparing the first one or two characters in the context with IV or CM or many other roman numeral combinations. If the match is true then I continue with further commands.
The format is
E.g., the string may be
and I want the first three characters,
test = "MMMCMXCIX" print(test[0: 3])
Outputs
or I want the last 4 characters
test = "MMMCMXCIX" print(test[-4:])
Outputs
or I want a section in the middle
test = "MMMCMXCIX" print(test[2:5])
Outputs
or stepped
test = "MMMCMXCIX" print(test[2:9:2])
Outputs
or even reversed
test = "MMMCMXCIX" print(test[::-1])
Outputs
The technique is very common in examples of Python source code throughout the internet. So, when you see the [] with numbers and colons inside, eg, [:-1:], it is likely to do with extracting a portion of a data structure.
Note that the technique also works on Lists and Tuples.
test = [1,2,3,4,5,6,7,8,9] print(test[0: 3]) print(test[-4:]) print(test[2:5]) print(test[2:9:2]) print(test[::-1]) print(test[:-1:])
Outputs
[1, 2, 3]
[6, 7, 8, 9]
[3, 4, 5]
[3, 5, 7, 9]
[9, 8, 7, 6, 5, 4, 3, 2, 1]
[1, 2, 3, 4, 5, 6, 7, 8]
Summary
... Refer to Book, pause Video Lectures or subscribe to Medium Membership to read textual content.