Issue #12760: Add a create mode to open(). Patch by David Townshend.
diff --git a/Modules/_io/_iomodule.c b/Modules/_io/_iomodule.c
index 6e8d374..f9bca1a 100644
--- a/Modules/_io/_iomodule.c
+++ b/Modules/_io/_iomodule.c
@@ -108,18 +108,19 @@
"mode is an optional string that specifies the mode in which the file\n"
"is opened. It defaults to 'r' which means open for reading in text\n"
"mode. Other common values are 'w' for writing (truncating the file if\n"
-"it already exists), and 'a' for appending (which on some Unix systems,\n"
-"means that all writes append to the end of the file regardless of the\n"
-"current seek position). In text mode, if encoding is not specified the\n"
-"encoding used is platform dependent. (For reading and writing raw\n"
-"bytes use binary mode and leave encoding unspecified.) The available\n"
-"modes are:\n"
+"it already exists), 'x' for creating and writing to a new file, and\n"
+"'a' for appending (which on some Unix systems, means that all writes\n"
+"append to the end of the file regardless of the current seek position).\n"
+"In text mode, if encoding is not specified the encoding used is platform\n"
+"dependent. (For reading and writing raw bytes use binary mode and leave\n"
+"encoding unspecified.) The available modes are:\n"
"\n"
"========= ===============================================================\n"
"Character Meaning\n"
"--------- ---------------------------------------------------------------\n"
"'r' open for reading (default)\n"
"'w' open for writing, truncating the file first\n"
+"'x' create a new file and open it for writing\n"
"'a' open for writing, appending to the end of the file if it exists\n"
"'b' binary mode\n"
"'t' text mode (default)\n"
@@ -130,7 +131,8 @@
"\n"
"The default mode is 'rt' (open for reading text). For binary random\n"
"access, the mode 'w+b' opens and truncates the file to 0 bytes, while\n"
-"'r+b' opens the file without truncation.\n"
+"'r+b' opens the file without truncation. The 'x' mode implies 'w' and\n"
+"raises an `FileExistsError` if the file already exists.\n"
"\n"
"Python distinguishes between files opened in binary and text modes,\n"
"even when the underlying operating system doesn't. Files opened in\n"
@@ -223,7 +225,7 @@
char *encoding = NULL, *errors = NULL, *newline = NULL;
unsigned i;
- int reading = 0, writing = 0, appending = 0, updating = 0;
+ int creating = 0, reading = 0, writing = 0, appending = 0, updating = 0;
int text = 0, binary = 0, universal = 0;
char rawmode[5], *m;
@@ -254,6 +256,9 @@
char c = mode[i];
switch (c) {
+ case 'x':
+ creating = 1;
+ break;
case 'r':
reading = 1;
break;
@@ -290,6 +295,7 @@
}
m = rawmode;
+ if (creating) *(m++) = 'x';
if (reading) *(m++) = 'r';
if (writing) *(m++) = 'w';
if (appending) *(m++) = 'a';
@@ -312,9 +318,9 @@
return NULL;
}
- if (reading + writing + appending > 1) {
+ if (creating + reading + writing + appending > 1) {
PyErr_SetString(PyExc_ValueError,
- "must have exactly one of read/write/append mode");
+ "must have exactly one of create/read/write/append mode");
return NULL;
}
@@ -408,7 +414,7 @@
if (updating)
Buffered_class = (PyObject *)&PyBufferedRandom_Type;
- else if (writing || appending)
+ else if (creating || writing || appending)
Buffered_class = (PyObject *)&PyBufferedWriter_Type;
else if (reading)
Buffered_class = (PyObject *)&PyBufferedReader_Type;
diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index 3829e0b..57cd9aa 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -46,6 +46,7 @@
typedef struct {
PyObject_HEAD
int fd;
+ unsigned int created : 1;
unsigned int readable : 1;
unsigned int writable : 1;
signed int seekable : 2; /* -1 means unknown */
@@ -152,6 +153,7 @@
self = (fileio *) type->tp_alloc(type, 0);
if (self != NULL) {
self->fd = -1;
+ self->created = 0;
self->readable = 0;
self->writable = 0;
self->seekable = -1;
@@ -290,15 +292,23 @@
s = mode;
while (*s) {
switch (*s++) {
- case 'r':
+ case 'x':
if (rwa) {
bad_mode:
PyErr_SetString(PyExc_ValueError,
- "Must have exactly one of read/write/append "
+ "Must have exactly one of create/read/write/append "
"mode and at most one plus");
goto error;
}
rwa = 1;
+ self->created = 1;
+ self->writable = 1;
+ flags |= O_EXCL | O_CREAT;
+ break;
+ case 'r':
+ if (rwa)
+ goto bad_mode;
+ rwa = 1;
self->readable = 1;
break;
case 'w':
@@ -988,6 +998,12 @@
static char *
mode_string(fileio *self)
{
+ if (self->created) {
+ if (self->readable)
+ return "xb+";
+ else
+ return "xb";
+ }
if (self->readable) {
if (self->writable)
return "rb+";
@@ -1049,15 +1065,17 @@
PyDoc_STRVAR(fileio_doc,
"file(name: str[, mode: str][, opener: None]) -> file IO object\n"
"\n"
-"Open a file. The mode can be 'r', 'w' or 'a' for reading (default),\n"
-"writing or appending. The file will be created if it doesn't exist\n"
-"when opened for writing or appending; it will be truncated when\n"
-"opened for writing. Add a '+' to the mode to allow simultaneous\n"
-"reading and writing. A custom opener can be used by passing a\n"
-"callable as *opener*. The underlying file descriptor for the file\n"
+"Open a file. The mode can be 'r', 'w', 'x' or 'a' for reading (default),\n"
+"writing, creating or appending. The file will be created if it doesn't\n"
+"exist when opened for writing or appending; it will be truncated when\n"
+"opened for writing. A `FileExistsError` will be raised if it already\n"
+"exists when opened for creating. Opening a file for creating implies\n"
+"writing so this mode behaves in a similar way to 'w'.Add a '+' to the mode\n"
+"to allow simultaneous reading and writing. A custom opener can be used by\n"
+"passing a callable as *opener*. The underlying file descriptor for the file\n"
"object is then obtained by calling opener with (*name*, *flags*).\n"
-"*opener* must return an open file descriptor (passing os.open as\n"
-"*opener* results in functionality similar to passing None).");
+"*opener* must return an open file descriptor (passing os.open as *opener*\n"
+"results in functionality similar to passing None).");
PyDoc_STRVAR(read_doc,
"read(size: int) -> bytes. read at most size bytes, returned as bytes.\n"