Tutorial for Getting Data from DXF Files

In this tutorial I show you how to get data from an existing DXF drawing.

At first load the drawing:

import ezdxf

dwg = ezdxf.readfile("your_dxf_file.dxf")

Layouts

I use the term layout as synonym for an arbitrary entity space which can contain any DXF construction element like LINE, CIRCLE, TEXT and so on. Every construction element has to reside in exact one layout.

There are three different layout types:

  • model space: this is the common construction place
  • paper space: used to to create printable drawings
  • block: reusable elements, every block has its own entity space

A DXF drawing consist of exact one model space and at least of one paper space. The DXF12 standard has only one unnamed paper space the later DXF standards can have more than one paper space and each paper space has a name.

Iterate over DXF Entities of a Layout

Iterate over all construction elements in the model space:

modelspace = dwg.modelspace()
for e in modelspace:
    if e.dxftype() == 'LINE':
        print("LINE on layer: %s\n" % e.dxf.layer)
        print("start point: %s\n" % e.dxf.start)
        print("end point: %s\n" % e.dxf.end)

All layout objects supports the standard Python iterator protocol and the in operator.

Access DXF Attributes of an Entity

Check the type of an DXF entity by e.dxftype(). The DXF type is always uppercase. All DXF attributes of an entity are grouped in the namespace e.dxf:

e.dxf.layer  # layer of the entity as string
e.dxf.color  # color of the entity as integer

See common DXF attributes:

If a DXF attribute is not set (a valid DXF attribute has no value), a ValueError will be raised. To avoid this use the GraphicEntity.get_dxf_attrib() method with a default value:

p = e.get_dxf_attrib('paperspace', 0)  # if 'paperspace' is left off, the entity defaults to model space

An unsupported DXF attribute raises an AttributeError.

Getting a Paper Space

paperspace = dwg.layout('layout0')

Retrieves the paper space named layout0, the usage of the layout object is the same as of the model space object. The DXF12 standard provides only one paper space, therefore the paper space name in the method call dwg.layout(‘layout0’) is ignored or can be left off. For the later standards you get a list of the names of the available layouts by Drawing.layout_names().

Iterate Over All DXF Entities at Once

Because the DXF entities of the model space and the entities of all paper spaces are stored in the ENTITIES section of the DXF drawing, you can also iterate over all drawing elements at once, except the entities placed in the block layouts:

for e in dwg.entities:
    print("DXF Entity: %s\n" % e.dxftype())

Retrieve Entities by Query Language

Inspired by the wonderful jQuery framework, I created a flexible query language for DXF entities. To start a query use the Layout.query() method, provided by all sort of layouts or use the ezdxf.query.new() function.

The query string is the combination of two queries, first the required entity query and second the optional attribute query, enclosed in square brackets: 'EntityQuery[AttributeQuery]'

The entity query is a whitespace separated list of DXF entity names or the special name *. Where * means all DXF entities, all other DXF names have to be uppercase. The attribute query is used to select DXF entities by its DXF attributes. The attribute query is an addition to the entity query and matches only if the entity already match the entity query. The attribute query is a boolean expression, supported operators: and, or, !.

Get all LINE entities from the model space:

modelspace = dwg.modelspace()
lines = modelspace.query('LINE')

The result container also provides the query() method, get all LINE entities at layer construction:

construction_lines = lines.query('*[layer=="construction"]')

The * is a wildcard for all DXF entities, in this case you could also use LINE instead of *, * works here because lines just contains entities of DXF type LINE.

All together as one query:

lines = modelspace.query('LINE[layer=="construction"]')

The ENTITIES section also supports the query() method:

all_lines_and_circles_at_the_construction_layer = dwg.entities.query('LINE CIRCLE[layer=="construction"]')

Get all model space entities at layer construction, but no entities with the linestyle DASHED:

not_dashed_entities = modelspace.query('*[layer=="construction" and linestyle!="DASHED"]')

Default Layer Settings

See also

Tutorial for Layers and class Layer