duplicates current cam and flips it horizontally. from https://pastecode.xyz/view/b7c34dda#L19

mirror_cam

import maya.cmds as mc
 
def createMirrorCam(currentCam):
    mirrorCam_grp = mc.group(empty=True,n="mirrorCam_grp")
    mc.addAttr(mirrorCam_grp, ln="notes", dt="string", sn="nts")
    mc.setAttr("%s.notes"%mirrorCam_grp, currentCam,type="string")
    mirrorCam = mc.duplicate (currentCam,n="mirrorCam")
    camPos = mc.xform(mirrorCam[0], ws=1, t=1, q=1)
    camRot = mc.xform(mirrorCam[0], ws=1, ro=1, q=1)
    mc.xform(mirrorCam_grp, ws=1, t=(camPos[0], camPos[1], camPos[2]),ro=(camRot[0], camRot[1], camRot[2]))
    mc.parentConstraint(currentCam,mirrorCam_grp)
   
    mc.setAttr("%s.scaleX"%(mirrorCam_grp),-1)
    mc.parent(mirrorCam,mirrorCam_grp,a=1)
   
    mc.setAttr("mirrorCam.rx", lock=False)
    mc.setAttr("mirrorCam.ry", lock=False)
    mc.setAttr("mirrorCam.rz", lock=False)
    mc.setAttr("mirrorCam.sx", lock=False)
    mc.setAttr("mirrorCam.sy", lock=False)
    mc.setAttr("mirrorCam.sz", lock=False)
   
    mc.setAttr("mirrorCam.rx", 0)
    mc.setAttr("mirrorCam.ry", 0)
    mc.setAttr("mirrorCam.rz", 0)
    mc.setAttr("mirrorCam.sx", 1)
    mc.setAttr("mirrorCam.sy", 1)
    mc.setAttr("mirrorCam.sz", 1)
       
    mc.lookThru('mirrorCam')
 
currentCam =mc.lookThru(q=1)
 
if currentCam == "mirrorCam":
    mc.lookThru(mc.getAttr("mirrorCam_grp.notes"))
    mc.delete("mirrorCam_grp")
else:
    sel = mc.ls(sl=1)
    if mc.objExists("mirrorCam_grp"):
        mc.delete("mirrorCam_grp")
    createMirrorCam(currentCam)
    mc.select(sel)