If you've never touched Python before or if you're just getting started, this post if for you. These are the things I simply can't live without being a Python programmer.
Don't use Python 2. Use Python 3.
There's no secret here. Just don't use Python 2.
Really, don't use it. Use Python 3.
Got it? Use Python 3.
No Python 2. Ever.
So you're learning Python. What's the first thing that you learn?
Hello World, okay.
But what's the second thing you learn? To me it's always summing up two integers. How do you do that in Python? Well, most people do something like this
first_int = int(input()) second_int = int(input()) print(first_int + second_int)
For that code, the input would look like so
12 # hit enter 3 # hit enter again # output 15
Forget about the last example for a bit. Let's say you want to do a code that gets two strings in one line and invert them like
# input hello world # enter (in one single line) # output world hello
You could use
first_string, second_string = input().split() print(second_string, first_string) # out: 'world hello'
split can also receive the delimiter characters as arguments. Let's say your strings are divided by a comma and a space like
To split those you could use
first_string, second_string = input().split(', ') print(second_string, ', ', first_string) # out: 'world, hello'
Mind the space on the
split(', '), not
In the last example we knew we were going to receive two strings as input. But what about when we don't know how many strings are there beforehand?
Let's say we want to make our code invert the order of all strings passed in the input, no matter how many are there
# input hello darkness my old friend # hit enter # output friend old my darkness hello # input just three strings # hit enter # output strings three just
You can use list comprehensions
all_strings = [string for string in input().split()] print(all_strings[::-1]) # all_strings[::-1] inverts the list
Going back to our first example (adding two integers), wouldn't it be better if we could pass in the two numbers in the same line?
If you need to read numbers instead of strings, you can use type casting
# Mind the int(a) converting each string to int first_int, second_int = [int(a) for a in input().split()] print(first_int + second_int) # Or convert to float first_float, second_float = [float(a) for a in input().split()] print(first_float + second_float)
Now what if we wanted to sum up as many numbers as come in the input? Like so
# input 1 2 # output 3 # input 2 3 3 4 # output 12
We read a list of integers and sum them up afterwards
# Mind the int(a) converting each string to int list_of_ints = [int(a) for a in input().split()] print(sum(list_of_ints))
This may also be useful in competitive programming or algorithm exercises when you have an input like
<number N> [list of N numbers]
2 9 8 # input 1 3 1 2 3 # input 2 4 8 9 8 7 # input 3
As in Python you don't need to know the length of a list beforehand (you could just use
len(my_list)), you can discard the first number of the list using slices
list_of_ints = [int(a) for a in input().split()][1:]
list_of_ints = [int(a) for a in input().split()] list_of_ints.pop(0)
If you're familiar with the C API for handling files, Python will seem very similar, but with all the features you always wanted in C.
First: opening, reading, writing, closing
# Open test_file.txt for writing (w) using an absolute path some_file = open('/home/gabriel/test_file.txt', 'w') # Open test_file.txt for reading (r) using a relative path some_other_file = open('test_file.txt', 'r') # Copy the content from some_other_file to some_file content = some_other_file.read() some_file.write(content) # Close files some_file.close() some_other_file.close()
Mind that, even though they seem like the same file,
some_other_file may not the same as
some_file because it's specified by a relative path instead of an absolute one
A better way of doing the above, however, is to use context managers, more specifically a
with open('/home/gabriel/test_file.txt', 'w') as some_file, \ open('test_file.txt', 'r') as some_other_file: # Copy the content from some_other_file to some_file content = some_other_file.read() some_file.write(content)
With that, you don't need to remind yourself of closing the file, the context manager does that for you when the
with statement finishes.