| 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() |