diff options
Diffstat (limited to 'lib/python2.7/StringIO.py')
| -rw-r--r-- | lib/python2.7/StringIO.py | 324 |
1 files changed, 324 insertions, 0 deletions
diff --git a/lib/python2.7/StringIO.py b/lib/python2.7/StringIO.py new file mode 100644 index 0000000..b63525b --- /dev/null +++ b/lib/python2.7/StringIO.py @@ -0,0 +1,324 @@ +r"""File-like objects that read from or write to a string buffer. + +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.truncate([size]) # truncate file at to at most size (default: current pos) +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). +- There's also a much faster implementation in C, called cStringIO, but + it's not subclassable. +- 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). +""" +try: + from errno import EINVAL +except ImportError: + EINVAL = 22 + +__all__ = ["StringIO"] + +def _complain_ifclosed(closed): + if closed: + raise ValueError, "I/O operation on closed file" + +class StringIO: + """class StringIO([buffer]) + + When a StringIO object is created, it can be initialized to an existing + string by passing the string to the constructor. If no string is given, + the StringIO will start empty. + + The StringIO object can accept either Unicode or 8-bit strings, but + mixing the two may take some care. If both are used, 8-bit strings that + cannot be interpreted as 7-bit ASCII (that use the 8th bit) will cause + a UnicodeError to be raised when getvalue() is called. + """ + def __init__(self, buf = ''): + # Force self.buf to be a string or unicode + if not isinstance(buf, basestring): + buf = str(buf) + self.buf = buf + self.len = len(buf) + self.buflist = [] + self.pos = 0 + self.closed = False + self.softspace = 0 + + def __iter__(self): + return self + + def next(self): + """A file object is its own iterator, for example iter(f) returns f + (unless f is closed). When a file is used as an iterator, typically + in a for loop (for example, for line in f: print line), the next() + method is called repeatedly. This method returns the next input line, + or raises StopIteration when EOF is hit. + """ + _complain_ifclosed(self.closed) + r = self.readline() + if not r: + raise StopIteration + return r + + def close(self): + """Free the memory buffer. + """ + if not self.closed: + self.closed = True + del self.buf, self.pos + + def isatty(self): + """Returns False because StringIO objects are not connected to a + tty-like device. + """ + _complain_ifclosed(self.closed) + return False + + def seek(self, pos, mode = 0): + """Set the file's current position. + + The mode argument is optional and defaults to 0 (absolute file + positioning); other values are 1 (seek relative to the current + position) and 2 (seek relative to the file's end). + + There is no return value. + """ + _complain_ifclosed(self.closed) + if self.buflist: + self.buf += ''.join(self.buflist) + self.buflist = [] + if mode == 1: + pos += self.pos + elif mode == 2: + pos += self.len + self.pos = max(0, pos) + + def tell(self): + """Return the file's current position.""" + _complain_ifclosed(self.closed) + return self.pos + + def read(self, n = -1): + """Read at most size bytes from the file + (less if the read hits EOF before obtaining size bytes). + + If the size argument is negative or omitted, read all data until EOF + is reached. The bytes are returned as a string object. An empty + string is returned when EOF is encountered immediately. + """ + _complain_ifclosed(self.closed) + if self.buflist: + self.buf += ''.join(self.buflist) + self.buflist = [] + if n is None or n < 0: + newpos = self.len + else: + newpos = min(self.pos+n, self.len) + r = self.buf[self.pos:newpos] + self.pos = newpos + return r + + def readline(self, length=None): + r"""Read one entire line from the file. + + A trailing newline character is kept in the string (but may be absent + when a file ends with an incomplete line). If the size argument is + present and non-negative, it is a maximum byte count (including the + trailing newline) and an incomplete line may be returned. + + An empty string is returned only when EOF is encountered immediately. + + Note: Unlike stdio's fgets(), the returned string contains null + characters ('\0') if they occurred in the input. + """ + _complain_ifclosed(self.closed) + if self.buflist: + self.buf += ''.join(self.buflist) + self.buflist = [] + i = self.buf.find('\n', self.pos) + if i < 0: + newpos = self.len + else: + newpos = i+1 + if length is not None and length >= 0: + if self.pos + length < newpos: + newpos = self.pos + length + r = self.buf[self.pos:newpos] + self.pos = newpos + return r + + def readlines(self, sizehint = 0): + """Read until EOF using readline() and return a list containing the + lines thus read. + + If the optional sizehint argument is present, instead of reading up + to EOF, whole lines totalling approximately sizehint bytes (or more + to accommodate a final whole line). + """ + total = 0 + lines = [] + line = self.readline() + while line: + lines.append(line) + total += len(line) + if 0 < sizehint <= total: + break + line = self.readline() + return lines + + def truncate(self, size=None): + """Truncate the file's size. + + If the optional size argument is present, the file is truncated to + (at most) that size. The size defaults to the current position. + The current file position is not changed unless the position + is beyond the new file size. + + If the specified size exceeds the file's current size, the + file remains unchanged. + """ + _complain_ifclosed(self.closed) + if size is None: + size = self.pos + elif size < 0: + raise IOError(EINVAL, "Negative size not allowed") + elif size < self.pos: + self.pos = size + self.buf = self.getvalue()[:size] + self.len = size + + def write(self, s): + """Write a string to the file. + + There is no return value. + """ + _complain_ifclosed(self.closed) + if not s: return + # Force s to be a string or unicode + if not isinstance(s, basestring): + s = str(s) + spos = self.pos + slen = self.len + if spos == slen: + self.buflist.append(s) + self.len = self.pos = spos + len(s) + return + if spos > slen: + self.buflist.append('\0'*(spos - slen)) + slen = spos + newpos = spos + len(s) + if spos < slen: + if self.buflist: + self.buf += ''.join(self.buflist) + self.buflist = [self.buf[:spos], s, self.buf[newpos:]] + self.buf = '' + if newpos > slen: + slen = newpos + else: + self.buflist.append(s) + slen = newpos + self.len = slen + self.pos = newpos + + def writelines(self, iterable): + """Write a sequence of strings to the file. The sequence can be any + iterable object producing strings, typically a list of strings. There + is no return value. + + (The name is intended to match readlines(); writelines() does not add + line separators.) + """ + write = self.write + for line in iterable: + write(line) + + def flush(self): + """Flush the internal buffer + """ + _complain_ifclosed(self.closed) + + def getvalue(self): + """ + Retrieve the entire contents of the "file" at any time before + the StringIO object's close() method is called. + + The StringIO object can accept either Unicode or 8-bit strings, + but mixing the two may take some care. If both are used, 8-bit + strings that cannot be interpreted as 7-bit ASCII (that use the + 8th bit) will cause a UnicodeError to be raised when getvalue() + is called. + """ + _complain_ifclosed(self.closed) + if self.buflist: + self.buf += ''.join(self.buflist) + self.buflist = [] + 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 =', repr(f.readline()) + print 'Position =', f.tell() + line = f.readline() + print 'Second line =', repr(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.truncate(length/2) + f.seek(0, 2) + print 'Truncated length =', f.tell() + if f.tell() != length/2: + raise RuntimeError, 'truncate did not adjust length' + f.close() + +if __name__ == '__main__': + test() |