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nt Module¶
The nt module exposes low-level Windows system calls. On Windows, os is
implemented on top of nt, exactly as it is implemented on top of
posix on Unix. Import os instead: it is the portable spelling
and provides the same functions.
nt exists only on Windows. On other platforms importing it raises
ModuleNotFoundError.
Complexity Reference¶
| Operation | Time | Space | Notes |
|---|---|---|---|
nt.open(path, flags, mode) |
O(1) + syscall | O(1) | Path lookup cost depends on filesystem |
nt.read(fd, n) |
O(n) + syscall | O(n) | n = bytes read |
nt.write(fd, data) |
O(n) + syscall | O(1) | n = bytes written |
nt.close(fd) |
O(1) + syscall | O(1) | Release descriptor |
nt.lseek(fd, pos, how) |
O(1) + syscall | O(1) | Adjust file offset |
nt.stat(path) |
O(1) + syscall | O(1) | Path lookup cost depends on filesystem |
nt.fstat(fd) |
O(1) + syscall | O(1) | Descriptor-based stat |
nt.listdir(path) |
O(m) + syscall | O(m) | m = directory entries returned |
nt.mkdir(path) |
O(1) + syscall | O(1) | Path lookup cost depends on filesystem |
nt.rmdir(path) |
O(1) + syscall | O(1) | Directory must be empty |
nt.unlink(path) |
O(1) + syscall | O(1) | Remove a file |
nt.rename(src, dst) |
O(1) + syscall | O(1) | Same-volume rename is metadata-only |
nt.getcwd() |
O(1) + syscall | O(1) | Current directory |
Complexity here describes work in the interpreter and the number of system calls. Actual wall-clock time is dominated by the filesystem and the kernel, not by Python.
Use os Instead¶
import os
# Portable: resolves to nt on Windows, posix on Unix
fd = os.open("example.txt", os.O_CREAT | os.O_WRONLY | os.O_TRUNC)
try:
os.write(fd, b"hello\n") # O(n) in bytes
finally:
os.close(fd)
entries = os.listdir(".") # O(m) in directory entries
Referencing nt directly pins the code to Windows for no benefit, since os
forwards to the same implementation.
Checking the Platform¶
import os
# The name of the underlying implementation module
print(os.name) # 'nt' on Windows, 'posix' elsewhere
# Prefer capability checks over platform checks where possible
if hasattr(os, "startfile"): # O(1) - Windows-only function
...
Windows only
nt is not importable on Linux or macOS. Write against os and check
os.name or feature availability rather than importing nt.
Version Notes¶
- All Python 3 versions:
ntbacksoson Windows; the split betweenntandposixis an implementation detail ofos - All versions: per-call complexity is unchanged; costs are dominated by the underlying Windows API