Sweater Pattern Generator

I'm a knitter and I enjoy creating things. When knitting a simple top-down raglan sweater, I found myself repeatedly reaching for spreadsheets to convert gauge, calculate increase schedules, and do all the rest of the math logic you typically have to deal with (or worse - do it all in my head and hope everything works out). This project started as an experiment: can the Excel charting workflow for a simple raglan pattern be automated in a modular fashion?

This library generates a complete top-down raglan sweater pattern from gauge and size inputs, producing human-readable instructions for cast-on, yoke shaping, separation, body, and sleeves.

What it does

Given a stitch gauge, row gauge, and size, the generator calculates:

• Cast-on stitch count with marker placement for raglan lines
• Yoke shaping with increase rounds spread evenly
• Back-neck short rows (optional) for better fit
• Separation of body and sleeves with underarm cast-on stitches
• Body worked straight from underarm to hem
• Sleeve shaping with decreases spread from underarm to cuff

Quick start

from sweater import Sweater

sw = Sweater(
    sts_per_10cm=22,
    rows_per_10cm=30,
    size="M",
    rib_pref=1,           # 1x1 ribbing
    use_short_rows=True,  # optional back-neck shaping
)

print(sw.render_text())

Run the test demo:

python -m sweater.test

Architecture

The library is organized around immutable plan objects that each handle one stage of the construction:

Module	Class	Purpose
caston.py	CastOnPlan	Data holder for neck stitch count and marker split
shortrows.py	ShortRowPlan	Back-neck short-row turn positions and instructions
yokeplan.py	YokePlan	Raglan increase schedule and stitch counts
separator.py	SeparatorPlan	Split body/sleeves, underarm cast-on
bodyplan.py	BodyPlan	Body length and optional waist shaping
sleeveplan.py	SleevePlan	Sleeve decreases from underarm to cuff

The Sweater class in raglan.py is the orchestrator that wires these plans together, handles short-row calculation, and produces the final pattern via render_text().

Shared numeric helpers (gauge conversions, rounding, spacing) live in helpers.py. Size constants (neck and chest circumferences) are defined in constants.py.

Configuration options

The Sweater class accepts the following parameters:

Parameter	Default	Description
sts_per_10cm	required	Stitch gauge per 10 cm
rows_per_10cm	required	Row gauge per 10 cm
size	required	Size key (XS, S, M, L, XL, XXL, XXXL)
rib_pref	1	Ribbing style: 0=none, 1=1x1, 2=2x2
neckband_cm	8.0	Neckband length in cm (worked in rib)
body_length_cm	40.0	Body length from underarm to hem
sleeve_length_cm	45.0	Sleeve length from underarm to cuff
use_short_rows	False	Enable back-neck short-row shaping
short_row_depth_cm	5.0	Depth of short-row section
underarm_cm	2.5	Underarm cast-on width in cm

TODO

• Add positive ease parameter (target range: 6-12 cm for bust)
• Account for underarm pickup stitches in sleeve construction
• Knit a test sweater using the generated instructions to validate the pattern
• Export to PDF or structured format