sympyのPiecewiseから式を取りだす方法を教えて下さい

(参考) 積分 - 読書ノート v1.4.0dev - プレハブ小屋
https://showa-yojyo.github.io/notebook/python-sympy/integrals.html

from sympy import *
var('s,t,x')
myLT1=laplace_transform(exp(-t), t, s)
print(myLT1)
myLT2=inverse_laplace_transform(myLT1[0], s, t)
print(myLT2)
#-------------------------------------------------------
myLT3=integrate(exp(-s*t), (t, 0, 1))
print(myLT3)
print(myLT3[1])
#-------------------------------------------------------
#(1/(s + 1), 0, True)
#exp(-t)*Heaviside(t)
#Piecewise((1, Eq(s, 0)), (1/s - exp(-s)/s, True))
#TypeError: 'Piecewise' object does not support indexing

1/s - exp(-s)/sを取りだす方法を教えて下さい。
よろしくお願いします。

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20180501 追記
full script :

from sympy import *
var('s,t')
myLT3=integrate(exp(-s*t), (t, 0, 1))
print(myLT3)
u = symbols('u', positive=True)
print(myLT3.subs(s, u).subs(u, s))
#Piecewise((1, Eq(s, 0)), (1/s - exp(-s)/s, True))
#1/s - exp(-s)/s

(参考) Piecewise - Wolfram Language Documentation
http://reference.wolfram.com/language/ref/Piecewise.html