QPEL(Query parameter expression language)

This package contains only qpelparser (tool capable of parsing qpel-formatted string as qpel.Token tree). No qpel formatter included
QPEL is simple context based language, it has only 3 element types:

• Getter - get value by key in dict or an attribute of an object
• Call - call target
• Literal - literal list/str/float/int

Getter

Non quoted string is a Getter. EXAMPLES:

• qqq - get value by key "qqq" or attribute by name "qqq" from context.
  Equivalent of context["qqq"] if isinstance(context, dict) else getattr(context, "qqq")
• QpelParser().parse("qqq").eval({'qqq': 42})) - returns 42

Getter elements can be chained with dot, EXAMPLES:

• qqq.www - get value by key "qqq" or attribute by name "qqq" from context and from that value get by "www".
  Equivalent of

val = context["qqq"] if isinstance(context, dict) else getattr(context, "qqq")
val["qqq"] if isinstance(val, dict) else getattr(val, "qqq")

• QpelParser().parse("qqq.bit_length").eval({'qqq': 42})) - returns <built-in method bit_length of int object>
• QpelParser().parse("qqq.www").eval({'qqq': {'www': 42}})) - returns 42

Call

Pair or round brackets is a Call. EXAMPLES:

• qqq() - get by "qqq" from context and call it without arguments/
  Equivalent of (context["qqq"] if isinstance(context, dict) else getattr(context, "qqq"))()
• QpelParser().parse("bit_length()").eval(42)) - returns 6 (bit representation of 42: '101010', 6 bits)

Everything inside round brackets is parsed as distinct qpel strings, separated by commas and used as arguments. EXAMPLES:

• a(b, c) - get "a" from context and call it with "b" and "c" from the context
• QpelParser().parse("a(b,c)").eval({'a':int,'b':'11','c':2})) - equivalent of int("11", 2), returns 3 (int accepts string with base)

Key arguments are also accepted. EXAMPLE:

• QpelParser().parse("dict(qqq=a,www=b)").eval({'dict': dict, 'a': 1, 'b': 2}) - returns {'qqq': 1, 'www': 2}

Literal

All other values are literals. EXAMPLES:

• 42 - int value 42
• 36.6 - float value 36.6
• 'qqq' - string value 'qqq', WARNING: only single quotes are accepted
• [] - empty list

Boolean values should present in context(implemented by Getter):

• QpelParser().parse("True").eval({"True": True}) - returns boolean True

Dictionaries are not supported. Could be changed later