很多时候，数据读写不一定是文件，也可以在内存中读写。 StringIO顾名思义就是在内存中读写str。 要把str写入StringIO，我们需要先创建一个StringIO，然后，像文件一样写入即可：.

OverviewThe module provides Python’s main facilities for dealing with varioustypes of I/O. There are three main types of I/O: text I/O, binary I/Oand raw I/O. These are generic categories, and various backing stores canbe used for each of them. A concrete object belonging to any of thesecategories is called a. Other common terms are streamand file-like object.Independent of its category, each concrete stream object will also havevarious capabilities: it can be read-only, write-only, or read-write. It canalso allow arbitrary random access (seeking forwards or backwards to anylocation), or only sequential access (for example in the case of a socket orpipe).All streams are careful about the type of data you give to them. For examplegiving a object to the write method of a binary streamwill raise a.

So will giving a object to thewrite method of a text stream. High-level Module Interface io. DEFAULTBUFFERSIZEAn int containing the default buffer size used by the module’s buffered I/Oclasses. Uses the file’s blksize (as obtained by) if possible.

Open ( file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None )This is an alias for the builtin function.This function raises an open witharguments path, mode and flags. The mode and flagsarguments may have been modified or inferred from the original call. Opencode ( path )Opens the provided file with mode 'rb'. This function should be usedwhen the intent is to treat the contents as executable code.path should be an absolute path.The behavior of this function may be overridden by an earlier call to the, however, it should always be consideredinterchangeable with open(path, 'rb').

Overriding the behavior isintended for additional validation or preprocessing of the file. NoteThe abstract base classes also provide default implementations of somemethods in order to help implementation of concrete stream classes. Forexample, provides unoptimized implementations ofreadinto and.At the top of the I/O hierarchy is the abstract base class. Itdefines the basic interface to a stream. Note, however, that there is noseparation between reading and writing to streams; implementations are allowedto raise if they do not support a given operation.The ABC extends. It deals with the readingand writing of bytes to a stream. Subclassesto provide an interface to files in the machine’s file system.The ABC deals with buffering on a raw byte stream.

Its subclasses, and buffer streams that arereadable, writable, and both readable and writable.provides a buffered interface to random access streams. Anothersubclass, is a stream of in-memorybytes.The ABC, another subclass of, deals withstreams whose bytes represent text, and handles encoding and decoding to andfrom strings., which extends it, is a buffered textinterface to a buffered raw stream. I/O Base Classes class io. IOBaseThe abstract base class for all I/O classes, acting on streams of bytes.There is no public constructor.This class provides empty abstract implementations for many methodsthat derived classes can override selectively; the defaultimplementations represent a file that cannot be read, written orseeked.Even though does not declare reador write because their signatures will vary, implementations andclients should consider those methods part of the interface. Also,implementations may raise a (or )when operations they do not support are called.The basic type used for binary data read from or written to a file is.

Other areaccepted as method arguments too. Text I/O classes work with data.Note that calling any method (even inquiries) on a closed stream isundefined. Implementations may raise in this case.(and its subclasses) supports the iterator protocol, meaningthat an object can be iterated over yielding the lines in astream. Lines are defined slightly differently depending on whether thestream is a binary stream (yielding bytes), or a text stream (yieldingcharacter strings). See below.is also a context manager and therefore supports thestatement.

In this example, file is closed after thewith statement’s suite is finished—even if an exception occurs. With open ( 'spam.txt', 'w' ) as file: file. Write ( 'Spam and eggs!'

)provides these data attributes and methods: close ( )Flush and close this stream. This method has no effect if the file isalready closed. Once the file is closed, any operation on the file(e.g.

Reading or writing) will raise a.As a convenience, it is allowed to call this method more than once;only the first call, however, will have an effect. ClosedTrue if the stream is closed. Fileno ( )Return the underlying file descriptor (an integer) of the stream if itexists. An is raised if the IO object does not use a filedescriptor. Flush ( )Flush the write buffers of the stream if applicable. This does nothingfor read-only and non-blocking streams.

Isatty ( )Return True if the stream is interactive (i.e., connected toa terminal/tty device). Readable ( )Return True if the stream can be read from. If False, readwill raise. Readline ( size=-1 )Read and return one line from the stream.

If size is specified, atmost size bytes will be read.The line terminator is always b'n' for binary files; for text files,the newline argument to can be used to select the lineterminator(s) recognized. Readlines ( hint=-1 )Read and return a list of lines from the stream. Hint can be specifiedto control the number of lines read: no more lines will be read if thetotal size (in bytes/characters) of all lines so far exceeds hint.Note that it’s already possible to iterate on file objects using for line in file. Without calling file.readlines.

Seek ( offset, whence=SEEKSET )Change the stream position to the given byte offset. Offset isinterpreted relative to the position indicated by whence. The defaultvalue for whence is SEEKSET. Values for whence are:.SEEKSET or 0 – start of the stream (the default);offset should be zero or positive.SEEKCUR or 1 – current stream position; offset maybe negative.SEEKEND or 2 – end of the stream; offset is usuallynegativeReturn the new absolute position. New in version 3.3: Some operating systems could support additional values, likeos.SEEKHOLE or os.SEEKDATA.

The valid valuesfor a file could depend on it being open in text or binary mode. Seekable ( )Return True if the stream supports random access.

If False, and will raise. Tell ( )Return the current stream position. Truncate ( size=None )Resize the stream to the given size in bytes (or the current positionif size is not specified).

The current stream position isn’t changed.This resizing can extend or reduce the current file size. In case ofextension, the contents of the new file area depend on the platform(on most systems, additional bytes are zero-filled). The new file sizeis returned. Changed in version 3.5: Windows will now zero-fill files when extending. Writable ( )Return True if the stream supports writing. If False,write and will raise.

Writelines ( lines )Write a list of lines to the stream. Line separators are not added, so itis usual for each of the lines provided to have a line separator at theend. del ( )Prepare for object destruction. Provides a defaultimplementation of this method that calls the instance’smethod. RawIOBaseBase class for raw binary I/O. There is nopublic constructor.Raw binary I/O typically provides low-level access to an underlying OSdevice or API, and does not try to encapsulate it in high-level primitives(this is left to Buffered I/O and Text I/O, described later in this page).In addition to the attributes and methods from,provides the following methods: read ( size=-1 )Read up to size bytes from the object and return them.

As a convenience,if size is unspecified or -1, all bytes until EOF are returned.Otherwise, only one system call is ever made. Fewer than size bytes maybe returned if the operating system call returns fewer than size bytes.If 0 bytes are returned, and size was not 0, this indicates end of file.If the object is in non-blocking mode and no bytes are available,None is returned.The default implementation defers to. Readall ( )Read and return all the bytes from the stream until EOF, using multiplecalls to the stream if necessary.

Readinto ( b )Read bytes into a pre-allocated, writableb, and return thenumber of bytes read. For example, b might be a.If the object is in non-blocking mode and no bytesare available, None is returned. Write ( b )Write the given, b, to theunderlying raw stream, and return the number ofbytes written.

This can be less than the length of b inbytes, depending on specifics of the underlying rawstream, and especially if it is in non-blocking mode. None isreturned if the raw stream is set not to block and no single byte couldbe readily written to it. The caller may release or mutate b afterthis method returns, so the implementation should only access bduring the method call. BufferedIOBaseBase class for binary streams that support some kind of buffering.It inherits. New in version 3.1.

Read ( size=-1 )Read and return up to size bytes. If the argument is omitted, None,or negative, data is read and returned until EOF is reached. An emptyobject is returned if the stream is already at EOF.If the argument is positive, and the underlying raw stream is notinteractive, multiple raw reads may be issued to satisfy the byte count(unless EOF is reached first).

But for interactive raw streams, at mostone raw read will be issued, and a short result does not imply that EOF isimminent.A is raised if the underlying raw stream is innon blocking-mode, and has no data available at the moment. Read1 ( size )Read and return up to size bytes, with at most one call to theunderlying raw stream’s (or) method. This can be useful if you areimplementing your own buffering on top of aobject.If size is -1 (the default), an arbitrary number of bytes arereturned (more than zero unless EOF is reached).

Readinto ( b )Read bytes into a pre-allocated, writableb and return the number of bytes read.For example, b might be a.Like, multiple reads may be issued to the underlying rawstream, unless the latter is interactive.A is raised if the underlying raw stream is in nonblocking-mode, and has no data available at the moment. Readinto1 ( b )Read bytes into a pre-allocated, writableb, using at most one call tothe underlying raw stream’s (or) method. Return the number of bytes read.A is raised if the underlying raw stream is in nonblocking-mode, and has no data available at the moment. New in version 3.5. Write ( b )Write the given, b, and return the numberof bytes written (always equal to the length of b in bytes, since ifthe write fails an will be raised).

Depending on theactual implementation, these bytes may be readily written to theunderlying stream, or held in a buffer for performance and latencyreasons.When in non-blocking mode, a is raised if thedata needed to be written to the raw stream but it couldn’t acceptall the data without blocking.The caller may release or mutate b after this method returns,so the implementation should only access b during the method call. Raw File I/O class io.

FileIO ( name, mode='r', closefd=True, opener=None )represents an OS-level file containing bytes data.It implements the interface (and therefore theinterface, too).The name can be one of two things:.a character string or object representing the path to thefile which will be opened. In this case closefd must be True (the default)otherwise an error will be raised.an integer representing the number of an existing OS-level file descriptorto which the resulting object will give access. When theFileIO object is closed this fd will be closed as well, unless closefdis set to False.The mode can be 'r', 'w', 'x' or 'a' for reading(default), writing, exclusive creation or appending. The file will becreated if it doesn’t exist when opened for writing or appending; it will betruncated when opened for writing.

Will be raised ifit already exists when opened for creating. Opening a file for creatingimplies writing, so this mode behaves in a similar way to 'w'. Add a'+' to the mode to allow simultaneous reading and writing.The read (when called with a positive argument), readintoand write methods on this class will only make one system call.A custom opener can be used by passing a callable as opener. The underlyingfile descriptor for the file object is then obtained by calling opener with( name, flags).

Opener must return an open file descriptor (passingas opener results in functionality similar to passingNone).The newly created file is.See the built-in function for examples on using the openerparameter. Buffered StreamsBuffered I/O streams provide a higher-level interface to an I/O devicethan raw I/O does. BytesIO ( initialbytes )A stream implementation using an in-memory bytes buffer.

The buffer is discarded when themethod is called.The optional argument initialbytes is a thatcontains initial data.provides or overrides these methods in addition to thosefrom and: getbuffer ( )Return a readable and writable view over the contents of the bufferwithout copying them. Also, mutating the view will transparentlyupdate the contents of the buffer. New in version 3.5.

BufferedReader ( raw, buffersize=DEFAULTBUFFERSIZE )A buffer providing higher-level access to a readable, sequentialobject. It inherits.When reading data from this object, a larger amount of data may berequested from the underlying raw stream, and kept in an internal buffer.The buffered data can then be returned directly on subsequent reads.The constructor creates a for the given readableraw stream and buffersize. If buffersize is omitted,is used.provides or overrides these methods in addition tothose from and: peek ( size )Return bytes from the stream without advancing the position. At most onesingle read on the raw stream is done to satisfy the call. The number ofbytes returned may be less or more than requested. Read ( size )Read and return size bytes, or if size is not given or negative, untilEOF or if the read call would block in non-blocking mode. Read1 ( size )Read and return up to size bytes with only one call on the raw stream.If at least one byte is buffered, only buffered bytes are returned.Otherwise, one raw stream read call is made.

Changed in version 3.7: The size argument is now optional. BufferedWriter ( raw, buffersize=DEFAULTBUFFERSIZE )A buffer providing higher-level access to a writeable, sequentialobject. It inherits.When writing to this object, data is normally placed into an internalbuffer.

The buffer will be written out to the underlyingobject under various conditions, including:.when the buffer gets too small for all pending data;.when is called;.when a seek is requested (for objects);.when the object is closed or destroyed.The constructor creates a for the given writeableraw stream. If the buffersize is not given, it defaults to.provides or overrides these methods in addition tothose from and: flush ( )Force bytes held in the buffer into the raw stream.

Ashould be raised if the raw stream blocks. Write ( b )Write the, b, and return thenumber of bytes written. When in non-blocking mode, ais raised if the buffer needs to be written out butthe raw stream blocks. BufferedRandom ( raw, buffersize=DEFAULTBUFFERSIZE )A buffered interface to random access streams. It inheritsand.The constructor creates a reader and writer for a seekable raw stream, givenin the first argument. If the buffersize is omitted it defaults to.is capable of anything orcan do. In addition, seek and tellare guaranteed to be implemented.

BufferedRWPair ( reader, writer, buffersize=DEFAULTBUFFERSIZE )A buffered I/O object combining two unidirectionalobjects – one readable, the other writeable – into a single bidirectionalendpoint. It inherits.reader and writer are objects that are readable andwriteable respectively. If the buffersize is omitted it defaults to.implements all of ’s methodsexcept for, which raises.

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Text I/O class io. TextIOBaseBase class for text streams. This class provides a character and line basedinterface to stream I/O. It inherits.There is no public constructor.provides or overrides these data attributes andmethods in addition to those from: encodingThe name of the encoding used to decode the stream’s bytes intostrings, and to encode strings into bytes. ErrorsThe error setting of the decoder or encoder. NewlinesA string, a tuple of strings, or None, indicating the newlinestranslated so far. Depending on the implementation and the initialconstructor flags, this may not be available.

BufferThe underlying binary buffer (a instance) thatdeals with. This is not part of theAPI and may not exist in some implementations. Detach ( )Separate the underlying binary buffer from the andreturn it.After the underlying buffer has been detached, the isin an unusable state.Some implementations, like, may nothave the concept of an underlying buffer and calling this method willraise. New in version 3.1.

Read ( size=-1 )Read and return at most size characters from the stream as a single. If size is negative or None, reads until EOF. Readline ( size=-1 )Read until newline or EOF and return a single str.

If the stream isalready at EOF, an empty string is returned.If size is specified, at most size characters will be read. Seek ( offset, whence=SEEKSET )Change the stream position to the given offset. Behaviour depends onthe whence parameter. The default value for whence isSEEKSET.SEEKSET or 0: seek from the start of the stream(the default); offset must either be a number returned by, or zero. Any other offset valueproduces undefined behaviour.SEEKCUR or 1: “seek” to the current position;offset must be zero, which is a no-operation (all other valuesare unsupported).SEEKEND or 2: seek to the end of the stream;offset must be zero (all other values are unsupported).Return the new absolute position as an opaque number. New in version 3.7.

Reconfigure (., encoding, errors, newline, linebuffering, writethrough )Reconfigure this text stream using new settings for encoding,errors, newline, linebuffering and writethrough.Parameters not specified keep current settings, excepterrors='strict' is used when encoding is specified buterrors is not specified.It is not possible to change the encoding or newline if some datahas already been read from the stream. On the other hand, changingencoding after write is possible.This method does an implicit stream flush before setting thenew parameters. New in version 3.7. StringIO ( initialvalue=', newline='n' )An in-memory stream for text I/O.

The text buffer is discarded when themethod is called.The initial value of the buffer can be set by providing initialvalue.If newline translation is enabled, newlines will be encoded as if. The stream is positioned at the start ofthe buffer.The newline argument works like that of.The default is to consider only n characters as ends of lines andto do no newline translation. If newline is set to None,newlines are written as n on all platforms, but universalnewline decoding is still performed when reading.provides this method in addition to those fromand its parents: getvalue ( )Return a str containing the entire contents of the buffer.Newlines are decoded as if by, althoughthe stream position is not changed.Example usage. Binary I/OBy reading and writing only large chunks of data even when the user asks for asingle byte, buffered I/O hides any inefficiency in calling and executing theoperating system’s unbuffered I/O routines. The gain depends on the OS and thekind of I/O which is performed. For example, on some modern OSes such as Linux,unbuffered disk I/O can be as fast as buffered I/O. The bottom line, however,is that buffered I/O offers predictable performance regardless of the platformand the backing device.

Therefore, it is almost always preferable to usebuffered I/O rather than unbuffered I/O for binary data. ReentrancyBinary buffered objects (instances of, and )are not reentrant. While reentrant calls will not happen in normal situations,they can arise from doing I/O in a handler. If a thread tries tore-enter a buffered object which it is already accessing, ais raised. Note this doesn’t prohibit a different thread from entering thebuffered object.The above implicitly extends to text files, since the functionwill wrap a buffered object inside a.

This includesstandard streams and therefore affects the built-in function aswell.