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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 _check_environ(variable, value):
 """check if a variable is present in the environmental variables"""

    if is_not_none(value):
        return value
    else:
        value = os.environ.get(variable)
        if is_none(value):
            stop(''.join([variable,
                          """ not supplied and no entry in environmental
                           variables"""]))
        else:
            return value