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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 Genome Examples
Variant data from the Thousand Genomes project is being served by the GA4GH reference server. In this example we show how to use the GA4GH client to access the data.
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:  We will continue to refer to this client object for accessing the remote server.
Access the dataset
Here, we issue or first API call to get a listing of datasets hosted by the server. The API call returns an iterator, which is iterated on once to get the 1kgenomes dataset.
Step2:  Access the reference set
The GA4GH Genomics API provides methods for accessing the bases of a reference. The Thousand Genomes data presented here are mapped to GRCh37.
To access these data we first list the reference sets.
Step3:  With the reference set saved to a variable we will now request for the available references. This is the list of contigs for which we can request reference bases.
Step4:  Here, we print the names of the available references. These reference names are used in the variants/search API. By selecting one of the references we can craft a ListBases request. Here, we ask for the 1000 bases between 10,000 and 11,000 on the first chromosome.
List reference bases
Step5:  List Variant Sets
The Thousand Genomes project sequenced the genome of over 2500 participants and released variation data in VCF format. The GA4GH reference server hosts those variant sets, and in this step we will list the available containers.
Step6:  There are two variant sets currently being made available by this server instance. release contains the calls for the each participant and functional_annotation provides details of the effects of these variants created using the Variant Effect Predictor.
Search variants
Now that we have stored identifiers for the variant sets hosted by this server, we can craft search requests to find the individual variants. The GA4GH genomics API closely follows VCF by providing the calls for each variant in the variant record itself. Let's get a single variant record to examine.
Step7:  Variant calls
Here, we select a few of the important fields of the variant record. Let's now examine the calls returned with this variant. The calls are what tell us which participants were believed to have presented the given variant.
Step8:  This tells us that for the participant HG00096 the variant in question was observed on the first haplotype ("genotype"
Step9:  Variant annotations
To get at the detailed variant annotations, we must first find the variant annotation set.
Step10:  We can now search for the range that includes our example variant to discover relevant annotations.
Step11:  Here we have found the annotation for our example variant and have found it has the upstream_gene_variant consequence.
Sequence annotations
Finally, we can learn more about the site of our example variant by querying the sequence annotations API, which is serving the Gencode Genes data.
Step12:  We can now craft search requests for features to find the nearest gene
Step13:  Querying read group set and reads from dataset
One can obtain read group set and their reads, by using the data set id, the group set name as well as the readgroup id, one can also provide a specific observance region, also we can provide a specific gene that we want to observe.
In this case we will use 0 as our starting point and 1,000,000 as our ending point, we will also be observing only the first chromosome. We will only be observing the first 2 subjects as means of demostration.
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Python Code:
import ga4gh.client as client
c = client.HttpClient("http://1kgenomes.ga4gh.org") 
Explanation: GA4GH 1000 Genome Examples
Variant data from the Thousand Genomes project is being served by the GA4GH reference server. In this example we show how to use the GA4GH client to access the data.
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
dataset = c.search_datasets().next()
print(dataset)
Explanation: We will continue to refer to this client object for accessing the remote server.
Access the dataset
Here, we issue or first API call to get a listing of datasets hosted by the server. The API call returns an iterator, which is iterated on once to get the 1kgenomes dataset.
End of explanation
reference_set = c.search_reference_sets().next()
print(reference_set)
Explanation: Access the reference set
The GA4GH Genomics API provides methods for accessing the bases of a reference. The Thousand Genomes data presented here are mapped to GRCh37.
To access these data we first list the reference sets.
End of explanation
references = [r for r in c.search_references(reference_set_id=reference_set.id)]
print(', '.join(sorted([reference.name for reference in references])))
Explanation: With the reference set saved to a variable we will now request for the available references. This is the list of contigs for which we can request reference bases.
End of explanation
chr1 = filter(lambda x: x.name == "1", references)[0]
bases = c.list_reference_bases(chr1.id, start=10000, end=11000)
print(bases)
print(len(bases))
Explanation: Here, we print the names of the available references. These reference names are used in the variants/search API. By selecting one of the references we can craft a ListBases request. Here, we ask for the 1000 bases between 10,000 and 11,000 on the first chromosome.
List reference bases
End of explanation
release = None
functional = None
for variant_set in c.search_variant_sets(dataset_id=dataset.id):
    if variant_set.name == "phase3-release":
        release = variant_set
    else:
        functional = variant_set
        
Explanation: List Variant Sets
The Thousand Genomes project sequenced the genome of over 2500 participants and released variation data in VCF format. The GA4GH reference server hosts those variant sets, and in this step we will list the available containers.
End of explanation
all_call_sets = list(c.search_call_sets(release.id))
call_set_ids = []
for call_set in all_call_sets:
    call_set_ids.append(str(call_set.id))
example_variant = c.search_variants(variant_set_id=release.id, start=10000, end=11000, reference_name=chr1.name, call_set_ids=call_set_ids).next()
print("Variant name: {}".format(example_variant.names[0]))
print("Start: {}, End: {}".format(example_variant.start, example_variant.end))
print("Reference bases: {}".format(example_variant.reference_bases))
print("Alternate bases: {}".format(example_variant.alternate_bases))
print("Number of calls: {}".format(len(example_variant.calls)))
Explanation: There are two variant sets currently being made available by this server instance. release contains the calls for the each participant and functional_annotation provides details of the effects of these variants created using the Variant Effect Predictor.
Search variants
Now that we have stored identifiers for the variant sets hosted by this server, we can craft search requests to find the individual variants. The GA4GH genomics API closely follows VCF by providing the calls for each variant in the variant record itself. Let's get a single variant record to examine.
End of explanation
print(example_variant.calls[0])
Explanation: Variant calls
Here, we select a few of the important fields of the variant record. Let's now examine the calls returned with this variant. The calls are what tell us which participants were believed to have presented the given variant.
End of explanation
total = 0
count = 0
for call in example_variant.calls:
    total += 1
    count += call.genotype[0] or call.genotype[1]
    
print("{}/{} participants with this variant".format(count, total))
print(float(count) / float(total))
Explanation: This tells us that for the participant HG00096 the variant in question was observed on the first haplotype ("genotype": [1, 0]). We can perform summary statistics on the calls field to measure allele frequency. For this demonstration we will count the presence of the variant on either haplotype to determine how often it was seen amongst the participants.
End of explanation
annotation_set = c.search_variant_annotation_sets(variant_set_id=functional.id).next()
Explanation: Variant annotations
To get at the detailed variant annotations, we must first find the variant annotation set.
End of explanation
annotation = c.search_variant_annotations(
    variant_annotation_set_id=annotation_set.id,
    start=example_variant.start,
    end=example_variant.end,
    reference_name=chr1.name).next()
print(annotation.transcript_effects[0].effects[0].term)
Explanation: We can now search for the range that includes our example variant to discover relevant annotations.
End of explanation
gencode = c.search_feature_sets(dataset_id=dataset.id).next()
print(gencode)
Explanation: Here we have found the annotation for our example variant and have found it has the upstream_gene_variant consequence.
Sequence annotations
Finally, we can learn more about the site of our example variant by querying the sequence annotations API, which is serving the Gencode Genes data.
End of explanation
gene = c.search_features(
    feature_set_id=gencode.id,
    start=10000,
    end=12000,
    reference_name="chr1",
    feature_types=['gene']).next()
print("Gene name: {}".format(gene.attributes.vals['gene_name'].values[0]))
print("Start: {}, End: {}".format(gene.start, gene.end))
Explanation: We can now craft search requests for features to find the nearest gene:
End of explanation
limit = 2
iterator = 0
read_group_set = c.search_read_group_sets(dataset_id=dataset.id).next()
print("Read group set : {}".format(read_group_set.name))
for read_group in read_group_set.read_groups:
    sequence = c.search_reads(read_group_ids=[read_group.id], start=0, end = 1000000, reference_id=references[0].id).next()
    print("Read group name: {},\nSequence: {}".format(read_group.name, sequence.aligned_sequence))
Explanation: Querying read group set and reads from dataset
One can obtain read group set and their reads, by using the data set id, the group set name as well as the readgroup id, one can also provide a specific observance region, also we can provide a specific gene that we want to observe.
In this case we will use 0 as our starting point and 1,000,000 as our ending point, we will also be observing only the first chromosome. We will only be observing the first 2 subjects as means of demostration.
End of explanation
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