How do I manually throw/raise an exception in Python? Use the most specific Exception constructor that semantically fits your issue. Be specific in your message, e.g.: raise ValueError(‘A very specific bad thing happened.’) Don’t raise generic exceptions Avoid raising a generic Exception. To catch it, you’ll have to catch all other more specific exceptions that … Read more
figure tells you the call signature: from matplotlib.pyplot import figure figure(figsize=(8, 6), dpi=80) figure(figsize=(1,1)) would create an inch-by-inch image, which would be 80-by-80 pixels unless you also give a different dpi argument.
os.remove() removes a file. os.rmdir() removes an empty directory. shutil.rmtree() deletes a directory and all its contents. Path objects from the Python 3.4+ pathlib module also expose these instance methods: pathlib.Path.unlink() removes a file or symbolic link. pathlib.Path.rmdir() removes an empty directory.
super() lets you avoid referring to the base class explicitly, which can be nice. But the main advantage comes with multiple inheritance, where all sorts of fun stuff can happen. See the standard docs on super if you haven’t already. Note that the syntax changed in Python 3.0: you can just say super().__init__() instead of … Read more
If you are not into long explanations, see Paolo Bergantino’s answer. Decorator Basics Python’s functions are objects To understand decorators, you must first understand that functions are objects in Python. This has important consequences. Let’s see why with a simple example : def shout(word=”yes”): return word.capitalize()+”!” print(shout()) # outputs : ‘Yes!’ # As an object, … Read more
The *args and **kwargs is a common idiom to allow arbitrary number of arguments to functions as described in the section more on defining functions in the Python documentation. The *args will give you all function parameters as a tuple: def foo(*args): for a in args: print(a) foo(1) # 1 foo(1,2,3) # 1 # 2 … Read more
This delays for 2.5 seconds: import time time.sleep(2.5) Here is another example where something is run approximately once a minute: import time while True: print(“This prints once a minute.”) time.sleep(60) # Delay for 1 minute (60 seconds).
To select rows whose column value equals a scalar, some_value, use ==: df.loc[df[‘column_name’] == some_value] To select rows whose column value is in an iterable, some_values, use isin: df.loc[df[‘column_name’].isin(some_values)] Combine multiple conditions with &: df.loc[(df[‘column_name’] >= A) & (df[‘column_name’] <= B)] Note the parentheses. Due to Python’s operator precedence rules, & binds more tightly than … Read more
new_list = my_list doesn’t actually create a second list. The assignment just copies the reference to the list, not the actual list, so both new_list and my_list refer to the same list after the assignment. To actually copy the list, you have several options: You can use the builtin list.copy() method (available since Python 3.3): … Read more
append appends a specified object at the end of the list: >>> x = [1, 2, 3] >>> x.append([4, 5]) >>> print(x) [1, 2, 3, [4, 5]] extend extends the list by appending elements from the specified iterable: >>> x = [1, 2, 3] >>> x.extend([4, 5]) >>> print(x) [1, 2, 3, 4, 5]