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POGenerating new expression from an existing expression in Z3
 

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  1. POGenerating new expression from an existing expression in Z3
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    <p>Given an expression f , I want to replace all variables <code>v</code> in <code>f</code> with something like <code>v_d</code> (<code>d</code> is a number). Currently I have to go through the following steps to achieve this </p> <ol> <li>Obtain all the variables in <code>f</code></li> <li>For each variable <code>v</code> in <code>f</code>, determine its sort, then generate the appropriate <code>v_d</code> var. </li> <li>do the substitution</li> </ol> <p>Since I am still trying to learn Z3 python so probably there is a much better way to do the above? </p> <p>Thanks.</p> <p>My full code is listed below:</p> <pre><code>def get_vars(f,rs=[]): """obtain variables from f""" if is_const(f): try: f.as_string() #to differentiate btw Int('x') and IntVal('3') return rs except AttributeError: return vset(rs + [f],str) else: for f_ in f.children(): rs = get_vars(f_,rs) return vset(rs,str) def gen_vars(vs,i): """ Generates a new set of variables E.g. v =&gt; v_i , v_next =&gt; v_(i+1) """ assert i&gt;=0 def mk_name(i,v): next_kw = '_next' if str(v).endswith(next_kw): astr = str(v)[:-len(next_kw)] + '_' + str(i+1) else: astr = str(v) + '_' + str(i) return astr def mk_var(name,vsort): if vsort.kind() == Z3_INT_SORT: v = Int(name) elif vsort.kind() == Z3_REAL_SORT: v = Real(name) elif vsort.kind() == Z3_BOOL_SORT: v = Bool(name) elif vsort.kind() == Z3_DATATYPE_SORT: v = Const(name,vsort) else: assert False, 'Cannot handle this sort yet (id: %d)'%vsort.kind() return v #so that the longest one is replaced first vs = sorted(vs,key=str,reverse=True) names = [mk_name(i,v) for v in vs] vs_ = [mk_var(ns,v.sort()) for ns,v in zip(names,vs)] vss = zip(vs,vs_) return vss def substitute_f(f,i,vs=None): """ Replaces all variables v in f with v_(i*_) vs: variables in f (could be automatically obtained from f) """ assert is_expr(f) assert isinstance(vs,list) or vs is None if vs is None: vs = get_vars(f) vss = gen_vars(vs,i) f_ = f for pvs in vss: f_ = substitute(f_,pvs) return f_ </code></pre>
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