Create a GUI on the terminal using curses

What is curses

According to the Official Documentation,

The curses library provides terminal-independent screen drawing and keyboard processing for text-based terminals (terminals) such as VT100s, Linux consoles, and emulation terminals provided by various programs. The terminal supports various control codes for performing common operations such as moving the cursor, scrolling the screen, and erasing the area. Different types of terminals may use very different control codes and often have a peculiar habit.

It may be useful when you want to create a simple GUI or when you want to work with server data that can only be accessed with ssh. You can also display the contents of CSV and DB.

Thing you want to do

For example, suppose you have the following csv file.

I would like to create a GUI that can display the contents on the terminal and select the prefecture to process.

Implementation

main.py

# -*- coding: utf-8 -*-
import curses
import csv
from math import ceil

ROWS_PER_PAGE = 20

ENTER = ord( "\n" )
ESC = 27
DOWN = curses.KEY_DOWN
UP = curses.KEY_UP

class UI():

    def __init__(self, header, rows):
        super().__init__()
        self.header = header 
        self.rows = rows
        #Initialization
        self.screen = curses.initscr()
        curses.noecho()
        curses.cbreak()
        curses.start_color()
        self.screen.keypad(1)
        #Color settings
        curses.init_pair(1, curses.COLOR_BLACK, curses.COLOR_CYAN)
        self.highlight_text = curses.color_pair(1) #Use the pair id in the line above
        self.normal_text = curses.A_NORMAL
        self.screen.border(0)
        curses.curs_set(0)
        self.rows_per_page = ROWS_PER_PAGE
        self.total_rows = len(self.rows)
        #Record the width of each column
        self.widths = []
        #Border drawing
        self.tavnit = '|'
        self.separator = '+'

        for index, title in enumerate(self.header):
            #Make the column title and the longest value of each row the width of the column
            max_col_length = max([len(row[index]) for row in self.rows])
            max_col_length = max(max_col_length, len(title))
            self.widths.append(max_col_length)

        #Border settings
        for w in self.widths:
            #It looks like this:
            # | %-2s | %-10s | %-10s | %-11s | %-9s | %-7s |
            self.tavnit += " %-"+"%ss |" % (w,)
            #It looks like this:
            # +----+------------+------------+-------------+-----------+---------+
            self.separator += '-'*w + '--+'

        self.total_pages = int(ceil(self.total_rows / self.rows_per_page))
        self.position = 1
        self.page = 1
        #Message to be displayed
        self.msg = 'Page: {}/{}'.format(self.page, self.total_pages)

    def end(self):
        curses.endwin()

    def draw(self):
        self.screen.erase()
        #Show message at the top
        self.screen.addstr(1, 2, self.msg, self.normal_text)
        #Border on the table
        self.screen.addstr(2, 2, self.separator, self.normal_text)
        #Show header
        self.screen.addstr(3, 2, self.tavnit % tuple(self.header), self.normal_text)
        #Border between header and content
        self.screen.addstr(4, 2, self.separator, self.normal_text)
        #Draw every line
        row_start = 1 + (self.rows_per_page * (self.page - 1))
        row_end = self.rows_per_page + 1 + (self.rows_per_page * (self.page - 1))
        for i in range(row_start, row_end):
            if i >= self.total_rows + 1:
                break
            row_number = i + (self.rows_per_page * (self.page - 1))
            #Highlight line
            if (row_number == self.position + (self.rows_per_page * (self.page - 1))):
                color = self.highlight_text
            else:
                color = self.normal_text
            #Since there are 4 lines such as messages and borders above+4
            draw_number = i - (self.rows_per_page * (self.page - 1)) + 4 #Since there are 4 lines such as messages and borders above
            self.screen.addstr(draw_number , 2, self.tavnit % tuple(self.rows[i - 1]), color)
        #Bottom border of the table,Since there are 4 lines such as messages and borders above+4
        bottom = min(row_end, self.total_rows + 1) - (self.rows_per_page * (self.page - 1)) + 4
        self.screen.addstr(bottom, 2, self.separator, self.normal_text)
        self.screen.refresh()

    def down(self):
        if self.page == self.total_pages:
            if self.position < self.total_rows:
                self.position += 1
        else:
            if self.position < self.rows_per_page + (self.rows_per_page * (self.page - 1)):
                self.position += 1
            else:
                self.page += 1
                self.position = 1 + (self.rows_per_page * (self.page - 1))
                self.msg = 'Page: {}/{}'.format(self.page, self.total_pages)
        self.draw()

    def up(self):
        if self.page == 1:
            if self.position > 1:
                self.position -= 1
        else:
            if self.position > (1 + (self.rows_per_page * (self.page - 1))):
                self.position -= 1
            else:
                self.page -= 1
                self.position = self.rows_per_page + (self.rows_per_page * (self.page - 1))
                self.msg = 'Page: {}/{}'.format(self.page, self.total_pages)
        self.draw()

    def esc(self):
        self.end()

    def enter(self):
        #What you want to do here
        prefecture_id = self.rows[self.position - 1][0]
        prefecture = self.rows[self.position - 1][1]
        self.msg = 'Page: {}/{} ({} {} was selected.)' \
                .format(self.page, self.total_pages, prefecture_id, prefecture)
        self.draw()

    def loop(self):
        #Detects the entered key
        key = self.screen.getch()
        while 1:
            if key == ENTER:
                self.enter()
            elif key == ESC:
                self.esc()
                break
            elif key == DOWN:
                self.down()
            elif key == UP:
                self.up()
            key = self.screen.getch()

if __name__ == '__main__':
    with open('prefectures.csv') as f:
        reader = csv.reader(f)
        data = list(reader)
    header = data[0]
    rows = data[1:]
    
    ui = UI(header, rows)
    ui.draw()
    ui.loop()

Run

$ python main.py

result

The maximum number of lines on the page is 20. You can scroll with ↑ and ↓. ʻEnter (return) will display the information of the corresponding prefecture in the message. Exit the GUI with ʻESC.