Two new generally useful modules: types defines names for all built-in types,

StringIO implements pseudo files writing into and reading from strings.

Lib/StringIO.py

@@ -0,0 +1,130 @@
+# class StringIO implements  file-like objects that read/write a
+# string buffer (a.k.a. "memory files").
+#
+# This implements (nearly) all stdio methods.
+#
+# f = StringIO()      # ready for writing
+# f = StringIO(buf)   # ready for reading
+# f.close()           # explicitly release resources held
+# flag = f.isatty()   # always false
+# pos = f.tell()      # get current position
+# f.seek(pos)         # set current position
+# f.seek(pos, mode)   # mode 0: absolute; 1: relative; 2: relative to EOF
+# buf = f.read()      # read until EOF
+# buf = f.read(n)     # read up to n bytes
+# buf = f.readline()  # read until end of line ('\n') or EOF
+# list = f.readlines()# list of f.readline() results until EOF
+# f.write(buf)        # write at current position
+# f.writelines(list)  # for line in list: f.write(line)
+# f.getvalue()        # return whole file's contents as a string
+#
+# Notes:
+# - Using a real file is often faster (but less convenient).
+# - fileno() is left unimplemented so that code which uses it triggers
+#   an exception early.
+# - Seeking far beyond EOF and then writing will insert real null
+#   bytes that occupy space in the buffer.
+# - There's a simple test set (see end of this file).
+
+import string
+
+class StringIO:
+	def __init__(self, buf = ''):
+		self.buf = buf
+		self.pos = 0
+		self.closed = 0
+	def close(self):
+		if not self.closed:
+			self.closed = 1
+			del self.buf, self.pos
+	def isatty(self):
+		return 0
+	def seek(self, pos, mode = 0):
+		if mode == 1:
+			pos = pos + self.pos
+		elif mode == 2:
+			pos = pos + len(self.buf)
+		self.pos = max(0, pos)
+	def tell(self):
+		return self.pos
+	def read(self, n = 0):
+		if n <= 0:
+			newpos = len(self.buf)
+		else:
+			newpos = min(self.pos+n, len(self.buf))
+		r = self.buf[self.pos:newpos]
+		self.pos = newpos
+		return r
+	def readline(self):
+		i = string.find(self.buf, '\n', self.pos)
+		if i < 0:
+			newpos = len(self.buf)
+		else:
+			newpos = i+1
+		r = self.buf[self.pos:newpos]
+		self.pos = newpos
+		return r
+	def readlines(self):
+		lines = []
+		line = self.readline()
+		while line:
+			lines.append(line)
+			line = self.readline()
+		return lines
+	def write(self, s):
+		if not s: return
+		if self.pos > len(self.buf):
+			self.buf = self.buf + '\0'*(self.pos - len(self.buf))
+		newpos = self.pos + len(s)
+		self.buf = self.buf[:self.pos] + s + self.buf[newpos:]
+		self.pos = newpos
+	def writelines(self, list):
+		self.write(string.joinfields(list, ''))
+	def getvalue(self):
+		return self.buf
+
+
+# A little test suite
+
+def test():
+	import sys
+	if sys.argv[1:]:
+		file = sys.argv[1]
+	else:
+		file = '/etc/passwd'
+	lines = open(file, 'r').readlines()
+	text = open(file, 'r').read()
+	f = StringIO()
+	for line in lines[:-2]:
+		f.write(line)
+	f.writelines(lines[-2:])
+	if f.getvalue() != text:
+		raise RuntimeError, 'write failed'
+	length = f.tell()
+	print 'File length =', length
+	f.seek(len(lines[0]))
+	f.write(lines[1])
+	f.seek(0)
+	print 'First line =', `f.readline()`
+	here = f.tell()
+	line = f.readline()
+	print 'Second line =', `line`
+	f.seek(-len(line), 1)
+	line2 = f.read(len(line))
+	if line != line2:
+		raise RuntimeError, 'bad result after seek back'
+	f.seek(len(line2), 1)
+	list = f.readlines()
+	line = list[-1]
+	f.seek(f.tell() - len(line))
+	line2 = f.read()
+	if line != line2:
+		raise RuntimeError, 'bad result after seek back from EOF'
+	print 'Read', len(list), 'more lines'
+	print 'File length =', f.tell()
+	if f.tell() != length:
+		raise RuntimeError, 'bad length'
+	f.close()
+
+if __name__ == '__main__':
+	test()