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/**

* @name String concatenation in loop

* @description Concatenating strings in loops has quadratic performance.

* @kind problem

* @tags efficiency

* maintainability

* @problem.severity recommendation

* @sub-severity low

* @precision low

* @id py/string-concatenation-in-loop

*/

import python

predicate string_concat_in_loop(BinaryExpr b) {

b.getOp() instanceof Add and

exists(SsaVariable d, SsaVariable u, BinaryExprNode add |

add.getNode() = b and d = u.getAnUltimateDefinition()

|

d.getDefinition().(DefinitionNode).getValue() = add and

u.getAUse() = add.getAnOperand() and

add.getAnOperand().pointsTo().getClass() = ClassValue::str()

)

}

from BinaryExpr b, Stmt s

where string_concat_in_loop(b) and s.getASubExpression() = b

select s, "String concatenation in a loop is quadratic in the number of iterations."