File Objects — Python 2.7.18 documentation

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# File Objects

Python’s built-in file objects are implemented entirely on the `FILE*` support from the C standard library. This is an implementation detail and may change in future releases of Python.

`PyFileObject`

  This subtype of `PyObject` represents a Python file object.

PyTypeObject `PyFile_Type`

  This instance of `PyTypeObject` represents the Python file type. This is exposed to Python programs as `file` and `types.FileType`.

int `PyFile_Check`(PyObject *p)

  Return true if its argument is a `PyFileObject` or a subtype of `PyFileObject`.

  Changed in version 2.2: Allowed subtypes to be accepted.

int `PyFile_CheckExact`(PyObject *p)

  Return true if its argument is a `PyFileObject`, but not a subtype of `PyFileObject`.

  New in version 2.2.

PyObject* `PyFile_FromString`(char *filename, char *mode)
  Return value: New reference.

  On success, return a new file object that is opened on the file given by filename, with a file mode given by mode, where mode has the same semantics as the standard C routine `fopen()`. On failure, return NULL.

PyObject* `PyFile_FromFile`(FILE *fp, char *name, char *mode, int (*close)(FILE*))
  Return value: New reference.

  Create a new `PyFileObject` from the already-open standard C file pointer, fp. The function close will be called when the file should be closed. Return NULL and close the file using close on failure. close is optional and can be set to NULL.

FILE* `PyFile_AsFile`(PyObject *p)

  Return the file object associated with p as a `FILE*`.

  If the caller will ever use the returned `FILE*` object while the GIL is released it must also call the `PyFile_IncUseCount()` and `PyFile_DecUseCount()` functions described below as appropriate.

void `PyFile_IncUseCount`(PyFileObject *p)

  Increments the PyFileObject’s internal use count to indicate that the underlying `FILE*` is being used. This prevents Python from calling f_close() on it from another thread. Callers of this must call `PyFile_DecUseCount()` when they are finished with the `FILE*`. Otherwise the file object will never be closed by Python.

  The GIL must be held while calling this function.

  The suggested use is to call this after `PyFile_AsFile()` and before you release the GIL:

      FILE *fp = PyFile_AsFile(p);
      PyFile_IncUseCount(p);
      /* ... */
      Py_BEGIN_ALLOW_THREADS
      do_something(fp);
      Py_END_ALLOW_THREADS
      /* ... */
      PyFile_DecUseCount(p);

  New in version 2.6.

void `PyFile_DecUseCount`(PyFileObject *p)

  Decrements the PyFileObject’s internal unlocked_count member to indicate that the caller is done with its own use of the `FILE*`. This may only be called to undo a prior call to `PyFile_IncUseCount()`.

  The GIL must be held while calling this function (see the example above).

  New in version 2.6.

PyObject* `PyFile_GetLine`(PyObject *p, int n)
  Return value: New reference.

  Equivalent to `p.readline([n])`, this function reads one line from the object p. p may be a file object or any object with a `readline()` method. If n is `0`, exactly one line is read, regardless of the length of the line. If n is greater than `0`, no more than n bytes will be read from the file; a partial line can be returned. In both cases, an empty string is returned if the end of the file is reached immediately. If n is less than `0`, however, one line is read regardless of length, but `EOFError` is raised if the end of the file is reached immediately.

PyObject* `PyFile_Name`(PyObject *p)
  Return value: Borrowed reference.

  Return the name of the file specified by p as a string object.

void `PyFile_SetBufSize`(PyFileObject *p, int n)

  Available on systems with `setvbuf()` only. This should only be called immediately after file object creation.

int `PyFile_SetEncoding`(PyFileObject *p, const char *enc)

  Set the file’s encoding for Unicode output to enc. Return `1` on success and `0` on failure.

  New in version 2.3.

int `PyFile_SetEncodingAndErrors`(PyFileObject *p, const char *enc, *errors)

  Set the file’s encoding for Unicode output to enc, and its error mode to err. Return `1` on success and `0` on failure.

  New in version 2.6.

int `PyFile_SoftSpace`(PyObject *p, int newflag)

  This function exists for internal use by the interpreter. Set the `softspace` attribute of p to newflag and return the previous value. p does not have to be a file object for this function to work properly; any object is supported (thought its only interesting if the `softspace` attribute can be set). This function clears any errors, and will return `0` as the previous value if the attribute either does not exist or if there were errors in retrieving it. There is no way to detect errors from this function, but doing so should not be needed.

int `PyFile_WriteObject`(PyObject *obj, PyObject *p, int flags)

  Write object obj to file object p. The only supported flag for flags is `Py_PRINT_RAW`; if given, the `str()` of the object is written instead of the `repr()`. Return `0` on success or `-1` on failure; the appropriate exception will be set.

int `PyFile_WriteString`(const char *s, PyObject *p)

  Write string s to file object p. Return `0` on success or `-1` on failure; the appropriate exception will be set.