d = {‘x’: 1, ‘y’: 2, ‘z’: 3} for key in d: print(key, ‘corresponds to’, d[key]) How does Python recognize that it needs only to read the key from the dictionary? Is key a special keyword, or is it simply a variable? 1 15
Given a list [“foo”, “bar”, “baz”] and an item in the list “bar”, how do I get its index 1? 3 39 >>> [“foo”, “bar”, “baz”].index(“bar”) 1 Reference: Data Structures > More on Lists Caveats follow Note that while this is perhaps the cleanest way to answer the question as asked, index is a rather … Read more
I need a good explanation (references are a plus) on Python slicing. 3 34 It’s pretty simple really: a[start:stop] # items start through stop-1 a[start:] # items start through the rest of the array a[:stop] # items from the beginning through stop-1 a[:] # a copy of the whole array There is also the step … Read more
What is the difference between a function decorated with @staticmethod and one decorated with @classmethod? 3 33 Maybe a bit of example code will help: Notice the difference in the call signatures of foo, class_foo and static_foo: class A(object): def foo(self, x): print(f”executing foo({self}, {x})”) @classmethod def class_foo(cls, x): print(f”executing class_foo({cls}, {x})”) @staticmethod def static_foo(x): … Read more
I want to flatten this list of lists: [[1, 2, 3], [4, 5, 6], [7], [8, 9]] into: [1, 2, 3, 4, 5, 6, 7, 8, 9] 2 28
How do I access the index in a for loop? xs = [8, 23, 45] for x in xs: print(“item #{} = {}”.format(index, x)) Desired output: item #1 = 8 item #2 = 23 item #3 = 45 2 22
What is the most elegant way to check if the directory a file is going to be written to exists, and if not, create the directory using Python? Here is what I tried: import os file_path = “/my/directory/filename.txt” directory = os.path.dirname(file_path) try: os.stat(directory) except: os.mkdir(directory) f = file(filename) Somehow, I missed os.path.exists (thanks kanja, Blair, … Read more
How do I call an external command within Python as if I’d typed it in a shell or command prompt? 6 63 Use the subprocess module in the standard library: import subprocess subprocess.run([“ls”, “-l”]) The advantage of subprocess.run over os.system is that it is more flexible (you can get the stdout, stderr, the “real” status … Read more
I want to merge two dictionaries into a new dictionary. x = {‘a’: 1, ‘b’: 2} y = {‘b’: 10, ‘c’: 11} z = merge(x, y) >>> z {‘a’: 1, ‘b’: 10, ‘c’: 11} Using x.update(y) modifies x in-place instead of creating a new dictionary. I also want the last-one-wins conflict-handling of dict.update() as well. … Read more
How do I check whether a file exists or not, without using the try statement? 3 39 If the reason you’re checking is so you can do something like if file_exists: open_it(), it’s safer to use a try around the attempt to open it. Checking and then opening risks the file being deleted or moved … Read more
