Generating a Code 39 barcode with Python

pyStrich is a Python library for generating Code 39 barcodes, along with other 1D and 2D symbologies.

Code 39 barcodes are widely used for industrial labelling. The default character set is uppercase letters, digits, space and -.$/+%; pass full_ascii=True to encode any 7-bit character as a pair of symbols.

Code39Encoder("17 E North 32 St", full_ascii=True).save("code39-address.png")

See also

Code 39 on Wikipedia for background on the symbology itself.

Code 39 barcodes are defined in ISO/IEC 16388.

Example

If you haven’t already installed pyStrich, you should do so – see Installation for more detail:

$ pip install pyStrich

Here’s how to generate a Code 39 barcode and save it as an SVG:

from pystrich.code39 import Code39Encoder

encoder = Code39Encoder("64755")
encoder.save_svg("code39-example.svg")
Code 39 barcode encoding "64755".

Sizing, label, font and layout

The bar_width argument to save() and get_imagedata() sets the pixel width of the narrowest bar (default 3).

The options dict passed to Code39Encoder controls the human-readable label and the surrounding layout. All keys are optional.

show_label

Whether to render the human-readable label underneath the bars. Defaults to True; set to False to suppress it.

ttf_font

Absolute path to a TrueType font file used for the label. Defaults to a bundled bitmap font if unset.

ttf_fontsize

Font size in points.

height

Total image height in pixels. Defaults to 120.

label_border

Pixels of vertical space between the bars and the label.

bottom_border

Pixels of vertical space between the label and the bottom edge.

See also

Printing barcodes for guidance on selecting bar_width for printed output.

options = {
    "height": 200,
    "label_border": 10,
    "bottom_border": 10,
    "ttf_fontsize": 24,
    # "ttf_font": "/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf",
}
encoder = Code39Encoder("64755", options=options)
encoder.save("code39-custom.png", bar_width=4)
Code 39 barcode encoding "64755" with a taller image and larger label.

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).

Code39Encoder("64755").save_svg("code39.svg")
SVG Code 39 barcode encoding "64755".

The SVG’s viewBox is in module units (one narrow bar = one unit), while width and height scale by bar_width. The 10-module quiet zones mandated by the standard are applied automatically on each side.

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.

Code39Encoder("64755").save("code39.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).

Code39Encoder("64755").save_eps("code39.eps")

The bar_width argument is the width of the narrowest bar in PostScript points (1 point = 1/72 inch). The 10-module quiet zones are applied automatically.

Added in version 0.12.

API

class Code39Encoder(text: str, full_ascii: bool = False, options: BarcodeRenderOptions | None = None)[source]

Bases: Bar1DEncoder

Encode a string as a Code 39 1D barcode.

By default only the standard Code 39 character set is accepted (0-9, A-Z, space, and -.$/+%). Pass full_ascii=True to use the Full ASCII extension, which encodes any 7-bit character via paired symbols.

Typical use:

encoder = Code39Encoder("ABC-123")
encoder.save("barcode.png")
Variables:

  • text – The original input text.

  • encoded_text – List of code values produced by the text encoder.

  • bars – The bar/space pattern as a string of "1" and "0".

  • options – Render-time options dict (empty if none were supplied).

  • width – Pixel width of the most recently rendered image.

  • height – Pixel height of the most recently rendered image.

get_eps(bar_width: int = 3, *, dark_hex: str | RGBA | None = None, light_hex: str | RGBA | None = None) → str[source]

Render the barcode and return EPS markup.

Parameters:

  • bar_width – Width in PostScript points of the narrowest bar.

  • dark_hex – Bar and text colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to black.

  • light_hex – Background colour as a 3-, 6- or 8-digit hex string or an RGBA, opaque. Defaults to white.

Return type:

str

Added in version 0.12.

Changed in version 0.16: Added dark_hex and light_hex.

get_imagedata(bar_width: int = 3, *, dark_hex: str | RGBA | None = None, light_hex: str | RGBA | None = None) → bytes[source]

Render the barcode and return PNG bytes.

Parameters:

  • bar_width – Width in pixels of the narrowest bar.

  • dark_hex – Bar and text colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to black.

  • light_hex – Background colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to white.

Returns:

PNG-encoded image data.

Return type:

bytes

Changed in version 0.16: Added dark_hex and light_hex.

get_pilimage(bar_width: int = 3, *, dark_hex: str | RGBA | None = None, light_hex: str | RGBA | None = None) → PILImage[source]

Render the barcode and return a Pillow image.

Parameters:

  • bar_width – Width in pixels of the narrowest bar.

  • dark_hex – Bar and text colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to black.

  • light_hex – Background colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to white.

Returns:

The rendered barcode.

Return type:

PIL.Image.Image

Added in version 0.11.

Changed in version 0.16: Added dark_hex and light_hex.

get_rect_marks() → SymbolMarks[source]

Return the barcode’s dark bars as rectangles in layout units.

Return type:

pystrich.marks.SymbolMarks

Added in version 0.18.

get_svg(bar_width: int = 3, *, dark_hex: str | RGBA | None = None, light_hex: str | RGBA | None = None) → str[source]

Render the barcode and return SVG markup.

Parameters:

  • bar_width – Width in user units of the narrowest bar.

  • dark_hex – Bar and text colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to black.

  • light_hex – Background colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to white.

Return type:

str

Added in version 0.12.

Changed in version 0.16: Added dark_hex and light_hex.

png_dataurl(bar_width: int = 3, *, dark_hex: str | RGBA | None = None, light_hex: str | RGBA | None = None) → str[source]

Render the barcode and return a PNG data: URL string.

Parameters:

  • bar_width – Width in pixels of the narrowest bar.

  • dark_hex – Bar and text colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to black.

  • light_hex – Background colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to white.

Return type:

str

Added in version 0.15.

Changed in version 0.16: Added dark_hex and light_hex.

save(filename: str | os.PathLike[str], bar_width: int = 3, *, dark_hex: str | RGBA | None = None, light_hex: str | RGBA | None = None) → None[source]

Render the barcode to a PNG file.

Parameters:

  • filename – Path to write the PNG to.

  • bar_width – Width in pixels of the narrowest bar.

  • dark_hex – Bar and text colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to black.

  • light_hex – Background colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to white.

Changed in version 0.16: Added dark_hex and light_hex.

save_eps(filename: str | os.PathLike[str], bar_width: int = 3, *, dark_hex: str | RGBA | None = None, light_hex: str | RGBA | None = None) → None[source]

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

Parameters:

  • filename – EPS output path.

  • bar_width – Width in PostScript points of the narrowest bar.

  • dark_hex – Bar and text colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to black.

  • light_hex – Background colour as a 3-, 6- or 8-digit hex string or an RGBA, opaque. Defaults to white.

Added in version 0.12.

Changed in version 0.16: Added dark_hex and light_hex.

save_svg(filename: str | os.PathLike[str], bar_width: int = 3, *, dark_hex: str | RGBA | None = None, light_hex: str | RGBA | None = None) → None[source]

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

Parameters:

  • filename – SVG output path.

  • bar_width – Width in user units of the narrowest bar.

  • dark_hex – Bar and text colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to black.

  • light_hex – Background colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to white.

Added in version 0.12.

Changed in version 0.16: Added dark_hex and light_hex.

svg_dataurl(bar_width: int = 3, *, dark_hex: str | RGBA | None = None, light_hex: str | RGBA | None = None) → str[source]

Render the barcode and return an SVG data: URL string.

Parameters:

  • bar_width – Width in user units of the narrowest bar.

  • dark_hex – Bar and text colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to black.

  • light_hex – Background colour as a 3-, 6- or 8-digit hex string or an RGBA. Defaults to white.

Return type:

str

Added in version 0.15.

Changed in version 0.16: Added dark_hex and light_hex.

init_renderer() → Code39Renderer[source]

Construct a Code39Renderer for the encoded bars.

Return type:

Code39Renderer