📄 08 – Python Basics Cheat Sheet¶
Quick reference — bookmark this and keep it open while coding!
Variables & Types¶
x = 42 # int
y = 3.14 # float
s = "hello" # str
b = True # bool
n = None # NoneType
type(x) # <class 'int'>
isinstance(x, int) # True
int("42") # 42
float("3.14") # 3.14
str(42) # "42"
Strings¶
s = "Hello, World!"
s.upper() # "HELLO, WORLD!"
s.lower() # "hello, world!"
s.strip() # remove whitespace
s.split(",") # ['Hello', ' World!']
",".join(["a","b"]) # "a,b"
s.replace("o","0") # "Hell0, W0rld!"
len(s) # 13
s[0] # 'H'
s[-1] # '!'
s[0:5] # 'Hello'
f"Val: {x:.2f}" # f-string formatting
Control Flow¶
if x > 0: # if
pass
elif x == 0: # else if
pass
else: # else
pass
y = "pos" if x > 0 else "neg" # ternary
for i in range(5): # 0,1,2,3,4
pass
for i, v in enumerate(lst): # index + value
pass
for a, b in zip(l1, l2): # parallel iteration
pass
while condition: # while loop
break # exit loop
continue # skip to next
Functions¶
def func(req, opt=10, *args, **kwargs):
return req
result = func("a", 20, 1, 2, x=5)
square = lambda x: x**2 # lambda
Lists¶
lst = [1, 2, 3]
lst.append(4) # [1,2,3,4]
lst.extend([5,6]) # [1,2,3,4,5,6]
lst.insert(0, 0) # [0,1,2,3,4,5,6]
lst.remove(3) # removes first 3
lst.pop() # removes+returns last
lst.sort() # sort in place
sorted(lst) # returns new sorted list
lst[::-1] # reversed copy
len(lst) # length
[x**2 for x in lst if x>2] # comprehension
Dictionaries¶
d = {"a": 1, "b": 2}
d["c"] = 3 # add/update
d.get("z", 0) # safe access, default 0
d.keys() # keys
d.values() # values
d.items() # (key, value) pairs
del d["a"] # delete key
d.pop("b") # remove + return
{k: v*2 for k,v in d.items()} # comprehension
Tuples & Sets¶
t = (1, 2, 3) # immutable
a, b, c = t # unpacking
s = {1, 2, 3, 2} # {1, 2, 3} — unique
s1 | s2 # union
s1 & s2 # intersection
s1 - s2 # difference
x in s # O(1) membership