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Given the following text description, write Python code to implement the functionality described below step by step
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Description:
 GA4GH 1000 Genomes Reference Service Example
This example illustrates how to access the available reference sequences offered by a GA4GH instance. 
Initialize the client
In this step we create a client object which will be used to communicate with the server. It is initialized using the URL.
Step1:  Search reference sets
Reference sets collect together named reference sequences as part of released assemblies. The API provides methods for accessing reference sequences.
The Thousand Genomes data presented here are mapped to GRCh37, and so this server makes that reference genome available. Datasets and reference genomes are decoupled in the data model, so it is possible to use the same reference set in multiple datasets.
Here, we list the details of the Reference Set.
Step2:  Obtaining individual Reference Sets by ID
The API can also obtain an individual reference set if the id is known. In this case, we can observe that only one is available. But in the future, more sets might be implemented.
Step3:  Search References
From the previous call, we have obtained the parameter required to obtain references which belong to ncbi37. We use its unique identifier to constrain the search for named sequences. As there are 86 of them, we have only chosen to show a few.
Step4:  Get Reference by ID
Reference sequence messages, like those above, can be referenced by their identifier directly. This identifier points to chromosome 1 in this server instance.
Step5:  List Reference Bases
Using the reference_id from above we can construct a query to list the alleles present on a sequence using start and end offsets.
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Python Code:
import ga4gh_client.client as client
c = client.HttpClient("http://1kgenomes.ga4gh.org")
Explanation: GA4GH 1000 Genomes Reference Service Example
This example illustrates how to access the available reference sequences offered by a GA4GH instance. 
Initialize the client
In this step we create a client object which will be used to communicate with the server. It is initialized using the URL.
End of explanation
for reference_set in c.search_reference_sets():
    ncbi37 = reference_set
    print "name: {}".format(ncbi37.name)
    print "ncbi_taxon_id: {}".format(ncbi37.ncbi_taxon_id)
    print "description: {}".format(ncbi37.description)
    print "source_uri: {}".format(ncbi37.source_uri)
Explanation: Search reference sets
Reference sets collect together named reference sequences as part of released assemblies. The API provides methods for accessing reference sequences.
The Thousand Genomes data presented here are mapped to GRCh37, and so this server makes that reference genome available. Datasets and reference genomes are decoupled in the data model, so it is possible to use the same reference set in multiple datasets.
Here, we list the details of the Reference Set.
End of explanation
reference_set = c.get_reference_set(reference_set_id=ncbi37.id)
print reference_set
Explanation: Obtaining individual Reference Sets by ID
The API can also obtain an individual reference set if the id is known. In this case, we can observe that only one is available. But in the future, more sets might be implemented.
End of explanation
counter = 0
for reference in c.search_references(reference_set_id="WyJOQ0JJMzciXQ"):
    counter += 1
    if counter > 5:
        break
    print reference
Explanation: Search References
From the previous call, we have obtained the parameter required to obtain references which belong to ncbi37. We use its unique identifier to constrain the search for named sequences. As there are 86 of them, we have only chosen to show a few.
End of explanation
reference = c.get_reference(reference_id="WyJOQ0JJMzciLCIxIl0")
print reference
Explanation: Get Reference by ID
Reference sequence messages, like those above, can be referenced by their identifier directly. This identifier points to chromosome 1 in this server instance.
End of explanation
reference_bases = c.list_reference_bases("WyJOQ0JJMzciLCIxIl0", start=15000, end= 16000)
print reference_bases
print len(reference_bases)
Explanation: List Reference Bases
Using the reference_id from above we can construct a query to list the alleles present on a sequence using start and end offsets.
End of explanation
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