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The weak two-pion form factor $F_V^{\pi\pi}$ is described as the product of aweak kernel $\cal{K}_W$ by a strong function $\Theta_{\pi\pi}^P$, determineddirectly from $\pi\pi$ scattering data. As the latter accounts at once for alleffects associated with resonances, intermediate $K\bar{K}$ loops, and otherpossible inelasticities present in $\pi\pi$ scattering, the need of modeling isrestricted to $\cal{K}_W$ only. The procedure proposed allows one to asses theweak kernel directly, which has a dominant cut beginning at the $K\bar{K}$threshold. Even the simplest vector-meson-dominance choice for $\cal{K}_W$already yields a good qualitative description of $F_V^{\pi\pi}$. The energysector below $0.8$ GeV is quite well reproduced when a precise theoreticalchiral perturbation $\pi\pi$ amplitude is used as input, together with thesingle free parameter $F_V G_V/F^2=1.20$. The inclusion of kaon loops, alongwell established lines and using few parameters, produces a good description ofthe form factor in the entire energy range allowed by $\tau$ decays. Thisindicates that the replacement of modeling by direct empirical scatteringinformation can also be useful in the construction of theoretical tools to beused in analysesof hadronic heavy meson decay data.

Electro-weak $\pi\pi$ form factor and $\pi\pi$ scattering: towards a phenomenological tool