Try to implement PipedGzipWriter.flush()

This doesn’t work.

See #8

tests/test_xopen.py

@@ -239,3 +239,13 @@ def test_bare_read_from_gz():
 def test_read_piped_gzip():
 	with PipedGzipReader('tests/hello.gz', 'rt') as f:
 		assert f.read() == 'hello'
+
+
+def test_flush():
+	with temporary_path('out.gz') as path:
+		f = xopen(path, 'wt')
+		f.write('hello')
+		f.flush()
+		# File is not closed here intentionally
+		f2 = xopen(path, 'rt')
+		assert f2.read() == 'hello'

xopen.py

@@ -94,6 +94,12 @@ def __init__(self, path, mode='wt'):
 	def write(self, arg):
 		self._file.write(arg)
 
+	def flush(self):
+		for i in range(3):  # because I don’t know in which order to do this
+			self.process.stdin.flush()
+			self.outfile.flush()
+			self._file.flush()
+
 	def close(self):
 		self.closed = True
 		self._file.close()