is is identity testing, == is equality testing. what happens in your code would be emulated in the interpreter like this: >>> a=”pub” >>> b = ”.join([‘p’, ‘u’, ‘b’]) >>> a == b True >>> a is b False so, no wonder they’re not the same, right? In other words: a is b is the … Read more
This should be as simple as: with open(‘somefile.txt’, ‘a’) as the_file: the_file.write(‘Hello\n’) From The Documentation: Do not use os.linesep as a line terminator when writing files opened in text mode (the default); use a single ‘\n’ instead, on all platforms. Some useful reading: The with statement open() ‘a’ is for append, or use ‘w’ to … Read more
You cannot declare a variable or value as constant in Python. To indicate to programmers that a variable is a constant, one usually writes it in upper case: CONST_NAME = “Name” To raise exceptions when constants are changed, see Constants in Python by Alex Martelli. Note that this is not commonly used in practice. As … Read more
Python never implicitly copies objects. When you set dict2 = dict1, you are making them refer to the same exact dict object, so when you mutate it, all references to it keep referring to the object in its current state. If you want to copy the dict (which is rare), you have to do so … Read more
The special variable __file__ contains the path to the current file. From that we can get the directory using either pathlib or the os.path module. Python 3 For the directory of the script being run: import pathlib pathlib.Path(__file__).parent.resolve() For the current working directory: import pathlib pathlib.Path().resolve() Python 2 and 3 For the directory of the … Read more
What is the line? You can just have arguments on the next line without any problems: a = dostuff(blahblah1, blahblah2, blahblah3, blahblah4, blahblah5, blahblah6, blahblah7) Otherwise you can do something like this: if (a == True and b == False): or with explicit line break: if a == True and \ b == False: Check … Read more
os.rename(), os.replace(), or shutil.move() All employ the same syntax: import os import shutil os.rename(“path/to/current/file.foo”, “path/to/new/destination/for/file.foo”) os.replace(“path/to/current/file.foo”, “path/to/new/destination/for/file.foo”) shutil.move(“path/to/current/file.foo”, “path/to/new/destination/for/file.foo”) Note that you must include the file name (file.foo) in both the source and destination arguments. If it is changed, the file will be renamed as well as moved. Note also that in the first two … Read more
import sys sys.exit() details from the sys module documentation: sys.exit([arg]) Exit from Python. This is implemented by raising the SystemExit exception, so cleanup actions specified by finally clauses of try statements are honored, and it is possible to intercept the exit attempt at an outer level. The optional argument arg can be an integer giving … Read more
Checking for __iter__ works on sequence types, but it would fail on e.g. strings in Python 2. I would like to know the right answer too, until then, here is one possibility (which would work on strings, too): try: some_object_iterator = iter(some_object) except TypeError as te: print(some_object, ‘is not iterable’) The iter built-in checks for … Read more
If you look at the docs for bytes, it points you to bytearray: bytearray([source[, encoding[, errors]]]) Return a new array of bytes. The bytearray type is a mutable sequence of integers in the range 0 <= x < 256. It has most of the usual methods of mutable sequences, described in Mutable Sequence Types, as … Read more