This node supports a fairly simple pattern language (similar to the Attribute from String node), alternating named “capture” groups and literal characters. The strings captured by the groups are assigned to attributes. This can be useful for parsing information formatted in a regular structure with separator characters.

For example, given a line in a file describing a set of attributes in the form:

"cat","cat0.png",1

You can parse the different parts into attributes using a pattern such as:

"{name}","{filename}.{}",{size:int}

(Empty braces capture a string but aren’t assigned to an attribute.)

• In the pattern, curly braces ({name}) match up to the next literal character in the pattern.

  • If the braces are empty, the matching string is thrown away.

  • The braces contain a name, the matching string is assigned to an attribute with that name. For exmaple, the part of the source string “captured” by {name} is assigned to the shot attribute.

  • If Infer attribute type is on, the node guesses the attribute type based on the matched string (if it looks like a whole number, it’s an integer; if it looks like a number with a decimal point, it’s a float; otherwise it’s a string). You can explicitly specify the type using {name:type}. For example, {shot:string}, {frame:int}, {time:float}.

  • Braces with no type or a string type only match text containing alphanumeric characters and underscores. Formally, they match text using the regex \w+.

• If you have capture braces at the end of the pattern, they match to the end of the source string.

• Outside braces, characters in the pattern must match characters in the source string exactly.

• Braces are not “greedy”… they only match up to the next literal character, even if going further would give a better match.

  For example, in day.01.csv, with the pattern {name}.csv you might expect {name} to capture day.01, but in fact it will only capture day (since it captures up to the next literal character, a period). The pattern will then fail because it expects the characters after the period to be csv, not 01.

• The whole pattern must match the source string (not just a prefix).

• If the whole pattern doesn’t match, none of the attributes in the pattern will be set.

For maximum power/flexibility, you can use a regular expression instead. This node uses Python’s regular expression syntax.

• Using a regular expression implies Infer attribute type.