How to Implement Pagination for LargeTable in Outfancy

Outfancy's Table class includes built-in pagination via the page parameter in render(), which internally calculates visible rows using check_page_value() and slices output through post_render() in outfancy/table.py.

The outfancy library provides terminal table formatting with native support for large datasets. Implementing pagination for LargeTable in outfancy requires no external dependencies—the Table class contains integrated logic to calculate page heights based on terminal dimensions and slice rendered output accordingly. This guide demonstrates how to use the built-in page argument and customize pagination behavior for CLI applications.

How Pagination Works in Outfancy

The pagination mechanism follows a three-step pipeline defined in outfancy/table.py:

Step 1: Request a Specific Page via render()

The render() method accepts a page argument (int | None) that specifies the zero-based page index to display【/tmp/instagit_umjxpk52/outfancy/table.py:260‑263】. When page is None, the entire table renders without slicing. When an integer is provided, the library calculates which rows belong to that page.

Step 2: Calculate Visible Rows with check_page_value()

Before rendering, check_page_value() determines the page_height by analyzing the terminal height (screen_y) and subtracting one line if a label row is present【/tmp/instagit_umjxpk52/outfancy/table.py:576‑589】. This ensures the table never exceeds the available terminal real estate.

Step 3: Slice the Rendered String in post_render()

After generating the full table string, post_render() splits the output into lines, extracts the slice from first_row to last_row based on the calculated page height, and rejoins the lines【/tmp/instagit_umjxpk52/outfancy/table.py:154‑168】. This sliced string is returned as the final output.

Basic Pagination Implementation

To paginate through a large dataset, instantiate the Table class and call render() with incrementing page values:

from outfancy.table import Table
from outfancy.example_dataset import dataset

tbl = Table()

# Optional: remove row limits to let terminal height dictate page size

tbl.set_maximum_number_of_rows(-1)

for page in range(3):
    rendered = tbl.render(dataset, page=page)
    print(f"\n--- Page {page + 1} ---")
    print(rendered)

How this works:

• page=0 displays the first screenful of rows
• check_page_value() automatically derives page_height from your terminal size
• post_render() handles the string slicing internally

Controlling Page Size and Layout

Fixed-Size Pages Regardless of Terminal Height

To enforce a specific number of rows per page (e.g., exactly 10 data rows), manually set screen_y to account for the header and margin:

from outfancy.table import Table
from outfancy.example_dataset import dataset

tbl = Table()
tbl.set_maximum_number_of_rows(-1)

# 10 data rows + 1 header + 1 margin = 12 lines

screen_y = 12

for i in range(0, len(dataset), 10):
    page_index = i // 10
    rendered = tbl.render(dataset, page=page_index, screen_y=screen_y)
    print(rendered)
    print("-" * 40)

Note: The library subtracts one line for the label row when label_list is present, leaving exactly 10 rows for data【/tmp/instagit_umjxpk52/outfancy/table.py:576‑589】.

Terminal-Responsive Pagination

For dynamic resizing based on the actual terminal dimensions, omit the screen_y argument or pass the current terminal height. The check_page_value() method recalculates page_height on each render() call, adapting to window resizing automatically.

Building an Interactive Pager

Create a command-line pager using a simple loop that adjusts the page parameter based on user input:

from outfancy.table import Table
from outfancy.example_dataset import dataset

tbl = Table()
current_page = 0

while True:
    output = tbl.render(dataset, page=current_page)
    print("\n" + output)
    
    cmd = input("\n[p]rev | [n]ext | [q]uit: ").strip().lower()
    if cmd == "n":
        current_page += 1
    elif cmd == "p" and current_page > 0:
        current_page -= 1
    elif cmd == "q":
        break

This implementation reuses the same render() logic—no manual slicing required.

Summary

• Built-in pagination is available via the page parameter in Table.render() at lines 260‑263 of outfancy/table.py
• Page height calculation occurs automatically in check_page_value() (lines 576‑589), respecting terminal dimensions and header rows
• Row slicing is handled by post_render() (lines 154‑168), which extracts the appropriate line range from the rendered string
• Customization is possible through set_maximum_number_of_rows() or explicit screen_y values to override terminal detection

Frequently Asked Questions

How do I disable pagination and show all rows at once?

Pass page=None (the default) to render(). When page is None, post_render() skips the slicing logic and returns the complete table string.

Can I limit the maximum rows per page independently of terminal size?

Yes. Call tbl.set_maximum_number_of_rows(n) where n is the desired limit, or pass a fixed screen_y value to render(). Setting -1 removes the limit entirely, allowing the terminal height to determine page size.

Where is the pagination logic implemented in the source code?

The core pagination logic resides in outfancy/table.py. Specifically, check_page_value() calculates how many rows fit on screen (lines 576‑589), while post_render() performs the actual string slicing to isolate the current page (lines 154‑168).

Does outfancy use zero-based or one-based page indexing?

Outfancy uses zero-based indexing for the page argument. The first page is 0, the second is 1, and so on. This aligns with Python's standard indexing conventions used throughout the library.

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