linkchecker/Template.py

"""String interpolation
20 Oct 1996
    Initial version called Itpl by Ka-Ping Yee
13 Jan 2000
    Modified by Bastian Kleineidam to emulate Perls Text::Template
   
Usage:
Template data consists of normal text and python code fragments.
Code fragments start with a dollar sign followed either by
1) variable or attribute reference or subscription or function call
   evaluates to the str() value of the given expression
   example: $printit()
   
2) {python statements}
   append arbitrary objects to the output list

Limitations:
1) Code fragments are arbitrary strings with matching "{}" parantheses.
   No further syntax verification is done.
2) Parameters to function calls must not have parantheses inside.
   Parameters to subscriptions must not have brackets inside.
   So this is not allowed:
   $func((tuple1,tuple2)) $func(map[key])
   But this is allowed:
   $func(param)[1] $a[x][y][z](blubb)
   In code fragments, you can write every Python code:
   ${OUT = OUT + trunk[idx[1](data())]}

Example:
import Template

t = Template.Template("blabla.tmpl")
open("blabla","w").write(t.fill_in({"var1":1,"var2":'hui'}))

blabla.tmpl:
Hello, this is a demo. var1 is $var1, and var2 is $var2.
"""
import sys, string, re
from types import StringType

# type argument (we cannot distinguish between filename and string type)
FILENAME = 0
ARRAY    = 1
FILE     = 2
STRING   = 3

# regular expressions for lexical analysis
# note we only match a subset of the language definition
# we match identifiers, attribute reference, subscriptions,
# slicings and function calls
identifier = "[a-zA-Z_][a-zA-Z0-9_]*"
attributeref = identifier + "(\." + identifier + ")*"
subscription = "\[.*\]"
callargs = "\(.*\)"
# now the whole regex
regexvar = re.compile("^"+attributeref+"("+subscription+"|"+callargs+")*")


class TemplateError(StandardError):
    pass


class Template:
    def __init__(self, data, argtype = FILENAME):
        "load the template in self.data"
        if argtype == FILENAME:
            file = open(data)
            self.data = string.join(file.readlines(), "")
            file.close()
        elif argtype == FILE:
            if data.closed:
                wasclosed = 1
                open(data)
            else:
                wasclosed = 0
            self.data = string.join(data.readlines(), "")
            if wasclosed:
                data.close()
        elif argtype == ARRAY:
            self.data = string.join(data, "\n")
        else:
            self.data = data
        if type(self.data) != StringType:
            raise TemplateError, "could not read data"


    def fill_in(self, dict={}):
        "parse the template and fill in values"
        try:
            namechars = 'abcdefghijklmnopqrstuvwxyz' \
                'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_';
            out = ""
            pos = 0
            while pos < len(self.data) and \
                  string.find(self.data, "$", pos) != -1:
                dollar = string.find(self.data, "$", pos)
                # append pure text without dollar
                out = out + self.data[pos:dollar]
                pos = dollar + 1
                nextchar = self.data[dollar+1]

                if nextchar == '{':
                    # apply a code fragment
                    level = 1
                    while level:
                        pos = pos + 1
                        if self.data[pos] == "{":
                            level = level + 1
                        elif self.data[pos] == "}":
                            level = level - 1
                    output = []
                    exec self.data[(dollar+2):pos] in dict, {"output":output}
                    for obj in output:
                        out = out + obj
                    pos = pos + 1

                elif nextchar in namechars:
                    # scan a variable access
                    var = regexvar.match(self.data[pos:])
                    if var:
                        # Houston, we have a match!
                        # extract the string and evaluate it
                        var = var.group()
                        pos = pos + len(var)
                        out = out + str(eval(var, dict))
                else:
                    if nextchar == "$":
                        pos = pos + 1
                        out = out + "$"

            if pos < len(self.data): 
                out = out + self.data[pos:]
        except:
            sys.stderr.write("Template.py: parse error at pos "+`pos`+":\n"+\
                             out+"\n")

        return out