print() outputs to console. input() reads from keyboard. # starts a comment.
name = input("Name: ")
print(f"Hello, {name}!") # f-string interpolation
x = 42 # int
pi = 3.14 # float
flag = True # bool
# if / elif / else
if x > 10:
print("big")
elif x > 0:
print("small")
else:
print("zero or negative")
# for loop
for i in range(5): # 0,1,2,3,4
print(i)
# while loop
while x > 0:
x -= 1
# function
def add(a, b):
return a + b
# list (mutable, ordered)
nums = [1, 2, 3]
nums.append(4) # [1,2,3,4]
nums[0] # 1
nums[-1] # 4
# tuple (immutable)
point = (10, 20)
# dict (key-value)
d = {"name": "Alice", "age": 25}
d["name"] # "Alice"
d.keys() # dict_keys(["name","age"])
# set (unique values)
s = {1, 2, 2, 3} # {1, 2, 3}
s = "hello world"
s.upper() # "HELLO WORLD"
s.lower() # "hello world"
s.split() # ["hello", "world"]
",".join(["a","b"]) # "a,b"
s.replace("hello","hi")# "hi world"
s.strip() # remove whitespace
s.find("world") # 6
s[::-1] # "dlrow olleh" (reverse)
len(s) # 11
lst = [3, 1, 2] lst.append(4) # [3,1,2,4] lst.pop() # removes 4 lst.sort() # [1,2,3] lst.reverse() # [3,2,1] lst[1:3] # [2,1] (slice) # list comprehension evens = [x for x in range(10) if x % 2 == 0] # [0, 2, 4, 6, 8] sorted([5,2,8], reverse=True) # [8,5,2]
# read
with open("file.txt", "r") as f:
content = f.read()
# write
with open("out.txt", "w") as f:
f.write("hello")
# append
with open("log.txt", "a") as f:
f.write("new line\n")
# read lines
with open("data.txt") as f:
for line in f:
print(line.strip())
import json
data = json.loads('{"a": 1}') # parse JSON string
text = json.dumps({"a": 1}) # to JSON string
import csv
# csv.reader, csv.writer
import os
os.getcwd() # current directory
os.listdir(".") # list files
os.path.exists("f") # check file
import sys
sys.argv # command line args