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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def getHosts(filename=None, hostlist=None):
 """Return a list of hosts depending on the environment"""

    if filename:
        return getHostsFromFile(filename)
    elif hostlist:
        return getHostsFromList(hostlist)
    elif getEnv() == "SLURM":
        return getHostsFromSLURM()
    elif getEnv() == "PBS":
        return getHostsFromPBS()
    elif getEnv() == "SGE":
        return getHostsFromSGE()
    else:
        return getDefaultHosts()