| 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() |
