QR Code¶

QR Code is a 2D symbology widely used for URLs and contact details.

Example¶

from pystrich.qrcode import QRCodeEncoder

encoder = QRCodeEncoder("https://github.com/mmulqueen/pyStrich")
encoder.save_svg("qrcode-example.svg")

QR code encoding the pyStrich GitHub URL.

Sizing and quiet zone¶

The cellsize argument to save() and get_imagedata() sets the pixel side length of one module (default 5).

Output formats¶

SVG output¶

For embedding in web pages or any workflow that benefits from resolution-independent output, use save_svg() (or get_svg() to receive the SVG as a string).

from pystrich.marks import MarkShape

QRCodeEncoder("https://github.com/mmulqueen/pyStrich").save_svg("qr.svg")
QRCodeEncoder("https://github.com/mmulqueen/pyStrich").save_svg(
    "qr-circles.svg", mark_shape=MarkShape.CIRCULAR_CELLS
)

Default	`mark_shape=MarkShape.CIRCULAR_CELLS`

The SVG’s viewBox is in module units, while width and height scale by cellsize. The mark_shape keyword selects how matched cells are drawn – horizontal runs of rectangles (the default) or one filled circle per cell.

Note

Circular cells fall outside the standard module shape and decoder support varies. Test with your target scanner before deploying.

Added in version 0.12.

PNG output¶

For raster output, use save() to write a PNG file or get_imagedata() to receive the raw PNG bytes.

QRCodeEncoder("https://github.com/mmulqueen/pyStrich").save("qrcode.png")

EPS output¶

For embedding in LaTeX (\includegraphics) or other vector print workflows, use save_eps() (or get_eps() to receive the EPS as a string).

QRCodeEncoder("https://github.com/mmulqueen/pyStrich").save_eps("qr.eps")

The cellsize argument is the side length of one module in PostScript points (1 point = 1/72 inch).

Added in version 0.12.

Terminal output¶

For quick on-screen display, get_terminal_art() returns a scannable rendering using Unicode half-block characters. Each character represents two matrix rows and one column, so cells appear roughly square in a typical fixed-width terminal font.

print(QRCodeEncoder("https://github.com/mmulqueen/pyStrich").get_terminal_art())

                                     
                                     
    █▀▀▀▀▀█ █▄█▀▀▀▄ ███▀▀ █▀▀▀▀▀█    
    █ ███ █ ▄▀██ ▀ █▀▄ ▀█ █ ███ █    
    █ ▀▀▀ █  ▄█▄█▀█▀▀▀▀█▄ █ ▀▀▀ █    
    ▀▀▀▀▀▀▀ █ ▀ ▀▄█ ▀▄█ ▀ ▀▀▀▀▀▀▀    
    █ ▀▀ ▀▀█ ▄█▄▀▀▀▀█▀▀▄▄ █▄▄▀ ▀█    
     ▄█ ▄▀▀▀█ ▄ ▀▄█▄▄▀█▄▄█▄▀▄ ▀▀▄    
    █▄ ▄█▄▀▀▀█▀█▀▄ ███ █  ▄  ▀█▄▄    
     ▀▄▄█ ▀▀  █▀▄▄▀▄█ ▀██▄█▄▄ ▀█▀    
    ▄▀▀▄██▀▄▀▀█ ▀▄ ▄▀ ▀▀▀  ▄▀█▄█     
    ▄█▄██ ▀▀█▄ █   █▀▄▄ ▀ ███ █      
    ▀  ▀ ▀▀▀▄▀██ █▄▄▄██ █▀▀▀███▄▄    
    █▀▀▀▀▀█ █▄▄▀ ▀  █ ▀▀█ ▀ ██ █▄    
    █ ███ █ ▄▄█▄▄ █▄█▀▀▄▀█▀██▄▀ ▄    
    █ ▀▀▀ █ ▀▀ ▀██ ▄▀▀▀ █▄ █ ▄▀▄▀    
    ▀▀▀▀▀▀▀ ▀▀ ▀ ▀▀ ▀ ▀▀▀▀▀    ▀     
                                     
                                     

By default the output is wrapped in ANSI escape codes that force a white background and black foreground, so the symbol scans regardless of the terminal’s colour scheme. Pass ansi_bg=False for plain output (correct only on a light-themed terminal).

Added in version 0.12.

DXF (CAD) output¶

For direct part marking applications, get_dxf() returns a DXF representation of the symbol that CAD and CAM tools can read directly. The cellsize is in your chosen units (default "mm") rather than pixels.

encoder = QRCodeEncoder("WDBCA45D2HA327260")
with open("part.dxf", "w") as f:
    f.write(encoder.get_dxf(cellsize=0.5, units="mm"))

The default inverse=True emits geometry for the light modules, including the quiet zone – so the bounding box frames the symbol. Pass inverse=False to emit only the dark modules instead, matching the symbol’s normal appearance; the bounding box then hugs the dark cells and the quiet zone has to be reintroduced downstream.

Error correction level¶

QR Codes embed redundant data so that a partly-damaged symbol can still be read. The error correction level (ECL) sets how much redundancy is added, and is one of:

`"L"`	Low: ~7% of codewords recoverable. Smallest symbol.
`"M"`	Medium: ~15%. Default if `ecl` is not supplied.
`"Q"`	Quartile: ~25%.
`"H"`	High: ~30%. Largest symbol; tolerates the most damage.

Higher levels produce a denser symbol for the same payload (or, equivalently, require a larger symbol to fit the same payload), so pick the lowest level that meets your durability needs. "H" is typically reserved for symbols that may be partly obscured (e.g. by a logo) or printed on surfaces likely to be scratched, smudged or torn.

QRCodeEncoder("https://en.wikipedia.org/wiki/Kings_River_(California)", ecl="H").save("qr-high.png")

GS1 Digital Link¶

GS1 Digital Link encodes a GTIN (with optional batch, expiry, serial, …) as a URL. It’s just a URL – pass it to QRCodeEncoder directly:

QRCodeEncoder("https://id.gs1.org/01/05050070007664/10/W126").save("dl.png")

Raw AI-syntax GS1 QR (FNC1 mode indicator) is not supported; for that, use Data Matrix.

Non-ASCII text¶

QRCodeEncoder accepts any Unicode string directly and picks the narrowest character set that fits. Wrap the input in QRCodeData only when you want to constrain that choice – for example, to enforce "ascii" so a stray non-ASCII character raises instead of silently growing the symbol:

Encoding	Behaviour
`"ascii"`	Raises `PyStrichInvalidInput` on any byte > 127.
`"iso-8859-1"`	Latin-1. Declares ECI 3 at the start of the symbol so decoders do not fall back to Shift-JIS heuristics on high bytes.
`"utf-8"`	Declares ECI 26 and byte-encodes the input. Conformant decoders pick up the encoding automatically.

Tip

The auto-selected encoding is always the narrowest one that fits, so passing a plain str already gives you the smallest symbol. Picking an encoding by hand is mostly useful for input validation – e.g. reject anything outside ASCII at the boundary.

# Plain str: Latin-1 picked automatically, ECI 3 emitted.
QRCodeEncoder("Ich dachte, Sie wären kräftiger").save("latin1.png")

# Plain str: UTF-8 picked automatically, ECI 26 emitted.
QRCodeEncoder("€5 親切にしろ 🐻‍❄️").save("utf8.png")

If you pin an encoding that does not fit the input, the raised error names the offending character and suggests the encoding that would have worked:

>>> from pystrich.qrcode import QRCodeData
>>> QRCodeData("Ich dachte, Sie wären kräftiger", encoding="ascii")
Traceback (most recent call last):
    ...
pystrich.exceptions.PyStrichInvalidInput: QRCodeData encoding 'ascii' expects ASCII; got 'ä'. Try QRCodeData('Ich dachte, Sie wären kräftiger', encoding='iso-8859-1') or pass auto_encoding=True to select an encoding automatically.

Anatomy¶

A QR Code carries the payload in a sea of data modules, surrounded by several fixed function patterns that let scanners locate, align and decode the symbol. The diagram below labels a Version 5 symbol (37x37 modules); larger versions repeat the same parts and add more alignment patterns, plus a version-information block from Version 7 upwards.

Annotated Version-5 QR Code showing the position detection patterns, separators, timing patterns, alignment pattern, data area and quiet zone.

Position detection patterns – the three large squares at the top-left, top-right and bottom-left corners. Scanners use them to detect the symbol from any angle and infer its orientation from the one missing corner.
Separators – a one-module strip of white isolating each finder from the data area, keeping the finder pattern unambiguous.
Timing patterns – one row and one column of alternating dark and light cells, running between the top finders and between the left finders. They fix the module grid across the symbol.
Alignment pattern – smaller squares dropped into the data area in Version 2 and above to correct for projective distortion when the symbol is photographed at an angle. Version 5 has one; the largest versions have several dozen.
Data and error correction – the masked codeword stream (payload plus Reed-Solomon). This is what scales with version.
Quiet zone – four modules of white margin on every side, as mandated by the QR Code specification.

API¶

class QRCodeEncoder(text: str | QRCodeData, ecl: Literal['L', 'M', 'Q', 'H'] | None = None)[source]¶

Bases: Matrix2DEncoder[int]

Encode text as a QR Code 2D barcode.

A plain str is encoded with the narrowest character set that fits: ASCII (no ECI), Latin-1 (ECI 3), or UTF-8 (ECI 26). Pass a QRCodeData to pin the encoding explicitly.

Typical use:

encoder = QRCodeEncoder("https://d-nb.info/gnd/135514053")
encoder.save("qr.png")

Variables:

matrix – 2D list describing the symbol prior to rendering.
width – Pixel width of the most recently rendered image.
height – Pixel height of the most recently rendered image.

init_renderer() → QRCodeRenderer[source]¶

Construct a QRCodeRenderer for the encoded matrix.

Updates width and height with the renderer’s dimensions and returns the renderer.

get_ascii() → str¶

Return an ASCII-art rendering of the symbol.

Return type:: str

get_dxf(cellsize: float = 1.0, inverse: bool = True, units: Literal['in', 'ft', 'mi', 'mm', 'cm', 'm'] | None = 'mm', *, mark_shape: MarkShape = MarkShape.SQUARE_CELLS) → str¶

Return a DXF (CAD) representation of the symbol.

Parameters:

cellsize – Side length of one module in units.
inverse – If True (the default), light modules are drawn as filled cells. If False, dark modules are drawn, matching the normal appearance of the symbol.
units – One of "in", "ft", "mi", "mm", "cm" or "m", or None for Unspecified ($INSUNITS=0).
mark_shape – How matched cells are grouped and drawn.

Return type:

str

Added in version 0.9.

Changed in version 0.12: units now supports "in", "ft", "mi", "cm", "m" and None (Unspecified); previously any value other than "mm" was silently treated as unspecified.

get_eps(cellsize: int = 5, *, inverse: bool = False, mark_shape: MarkShape = MarkShape.HORIZONTAL_RUNS) → str¶

Render the symbol and return EPS markup.

Parameters:

cellsize – Side length in PostScript points of one module.
inverse – If True, mark the light cells instead of the dark ones.
mark_shape – How matched cells are grouped and drawn.

Return type:

str

Added in version 0.12.

get_imagedata(cellsize: int = 5) → bytes¶

Render the symbol and return PNG bytes.

Parameters:: cellsize – Side length in pixels of one module.
Returns:: PNG-encoded image data.
Return type:: bytes

get_pilimage(cellsize: int = 5) → PIL.Image.Image¶

Render the symbol and return a Pillow image.

Parameters:: cellsize – Side length in pixels of one module.
Returns:: The rendered symbol.
Return type:: PIL.Image.Image

Added in version 0.11.

get_svg(cellsize: int = 5, *, inverse: bool = False, mark_shape: MarkShape = MarkShape.HORIZONTAL_RUNS) → str¶

Render the symbol and return SVG markup.

Parameters:

cellsize – Side length in user units of one module.
inverse – If True, mark the light cells instead of the dark ones.
mark_shape – How matched cells are grouped and drawn.

Return type:

str

Added in version 0.12.

get_terminal_art(*, ansi_bg: bool = True) → str¶

Render the symbol using Unicode half-block characters for terminals.

Each character represents two matrix rows and one column, producing approximately square cells in a typical fixed-width font and yielding a result that is scannable on screen.

Parameters:: ansi_bg – If True (the default), wrap each line in ANSI escape codes that force a white background and black foreground, making the symbol scannable regardless of the terminal’s colour scheme. Set to False for plain output (correct only on a light-themed terminal).
Return type:: str

Added in version 0.12.

save(filename: str | PathLike[str], cellsize: int = 5) → None¶

Save the symbol as a PNG. Pass a .png filename.

Parameters:

filename – PNG output path.
cellsize – Side length in pixels of one module.

save_eps(filename: str | PathLike[str], cellsize: int = 5, *, inverse: bool = False, mark_shape: MarkShape = MarkShape.HORIZONTAL_RUNS) → None¶

Save the symbol as an EPS file. Pass an .eps filename.

Parameters:

filename – EPS output path.
cellsize – Side length in PostScript points of one module.
inverse – If True, mark the light cells instead of the dark ones.
mark_shape – How matched cells are grouped and drawn.

Added in version 0.12.

save_svg(filename: str | PathLike[str], cellsize: int = 5, *, inverse: bool = False, mark_shape: MarkShape = MarkShape.HORIZONTAL_RUNS) → None¶

Save the symbol as an SVG file. Pass a .svg filename.

Parameters:

filename – SVG output path.
cellsize – Side length in user units of one module.
inverse – If True, mark the light cells instead of the dark ones.
mark_shape – How matched cells are grouped and drawn.

Added in version 0.12.

class QRCodeData(*segments: str, encoding: Literal['ascii', 'iso-8859-1', 'utf-8'] | None = None, auto_encoding: bool = False)¶

Bases: object

Encoder input with an explicit character-set choice.

QRCodeEncoder accepts a plain str and selects the encoding automatically. Use QRCodeData only to pin the encoding – for example, force "ascii" to reject non-ASCII input.

Pass either encoding= (one of "ascii", "iso-8859-1", "utf-8") or auto_encoding=True. With auto_encoding=True the constructor picks the narrowest fitting encoding; any encoding= argument is then ignored.

Variables:

segments – Tuple of input string segments.
encoding – The chosen Python codec name.
auto_encoding – True if the encoding was picked automatically.