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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 parse_env_var(s):
 """Parse an environment variable string Returns a key-value tuple Apply the same logic as `docker run -e`: "If the operator names an environment variable without specifying a value, then the current value of the named variable is propagated into the container's environment """

    parts = s.split('=', 1)
    if len(parts) == 2:
        k, v = parts
        return (k, v)

    k = parts[0]
    return (k, os.getenv(k, ''))