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# VCF File Writing
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Functionality for writing VCF records to files while preserving metadata integrity and VCF format compliance.
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## Capabilities
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### VCF Writer
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Write VCF records to files with proper formatting and metadata preservation.
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```python { .api }
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class Writer:
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    def __init__(self, stream, template, lineterminator="\n"):
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        """
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        Initialize VCF writer.
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        Parameters:
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        - stream: file-like object, output stream
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        - template: Reader object, provides header metadata and format
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        - lineterminator: str, line ending character(s)
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        """
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    def write_record(self, record):
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        """
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        Write a variant record to the output file.
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        Parameters:
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        - record: _Record object to write
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        """
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    def flush(self):
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        """Flush the output stream."""
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    def close(self):
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        """Close the output stream."""
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```
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### Backwards Compatibility
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```python { .api }
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class VCFWriter:
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    """Alias for Writer class for backwards compatibility."""
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    pass
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```
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### Usage Examples
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```python
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import vcf
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# Basic VCF writing
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reader = vcf.Reader(filename='input.vcf')
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writer = vcf.Writer(open('output.vcf', 'w'), reader)
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for record in reader:
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    # Optional: modify record
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    if record.QUAL and record.QUAL > 30:
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        writer.write_record(record)
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writer.close()
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# Writing filtered records
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reader = vcf.Reader(filename='input.vcf')
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with open('filtered.vcf', 'w') as output_file:
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    writer = vcf.Writer(output_file, reader)
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    for record in reader:
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        # Filter by variant type
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        if record.is_snp:
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            writer.write_record(record)
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    writer.flush()
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# Copy with modifications
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reader = vcf.Reader(filename='input.vcf')
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writer = vcf.Writer(open('modified.vcf', 'w'), reader)
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for record in reader:
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    # Add INFO field
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    record.INFO['PROCESSED'] = True
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    writer.write_record(record)
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writer.close()
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```