Python Tutorial (2): Tipe Data, Variabel, dan Operator

nama_lengkap = "Alice"    # snake_case (standar Python)
umur2 = 25                # angka OK, tidak di awal
_private = "internal"     # konvensi: leading underscore = internal
 
# TIDAK valid:
# 2nama = "x"             # SyntaxError: diawali angka
# class = "x"             # SyntaxError: kata kunci
# my-var = 1              # SyntaxError: minus bukan underscore

nama = "Alice"          # str
umur = 25               # int
tinggi = 165.5          # float
aktif = True            # bool
 
# Multiple assignment
x, y, z = 1, 2, 3
a = b = c = 0
 
# Type check
type(nama)    # <class 'str'>
isinstance(umur, int)   # True

# Integer: presisi tak terbatas
besar = 10**100
biner = 0b1010      # 10
oktal = 0o17        # 15
heksa = 0xFF        # 255
 
# Float: IEEE 754 double precision
pi = 3.14159
scientific = 1.5e-3   # 0.0015
 
# Operasi
10 / 3      # 3.3333 (true division)
10 // 3     # 3 (floor division)
10 % 3      # 1 (modulo)
2 ** 10     # 1024 (power)
 
# Konversi
int("42")       # 42
float("3.14")   # 3.14
int(3.99)       # 3 (truncate, bukan round)
round(3.7)      # 4

s = "Hello, World"
s2 = 'Single quotes juga OK'
multi = """String
multi-baris"""
 
# Indexing & slicing
s[0]        # 'H'
s[-1]       # 'd'
s[0:5]      # 'Hello'
s[7:]       # 'World'
s[::-1]     # 'dlroW ,olleH' (reverse)
 
# Methods
"hello".upper()              # 'HELLO'
"  spaces  ".strip()         # 'spaces'
"a,b,c".split(",")          # ['a', 'b', 'c']
", ".join(["a", "b", "c"])  # 'a, b, c'
"hello".replace("l", "L")   # 'heLLo'
"hello world".title()        # 'Hello World'
"abc123".isalnum()           # True
 
# f-string (Python 3.6+): format terbaik
name = "Alice"
age = 30
f"Nama: {name}, Umur: {age}"
f"Pi = {3.14159:.2f}"        # 'Pi = 3.14'
f"{'center':^20}"            # '      center      '
 
# Escape characters
print("Baris pertama\nBaris kedua")   # newline
print("Tab\tseparated")               # tab
print("Quote: \"hello\"")             # escaped quote
print(r"C:\Users\Alice")             # raw string, backslash literal
 
# Format alternatif
"Nama: {}, Umur: {}".format(name, age)
"Nama: {n}, Umur: {a}".format(n=name, a=age)
"Pi = {:.2f}".format(3.14159)

10 + 3    # 13
10 - 3    # 7
10 * 3    # 30
10 / 3    # 3.333... (true division, selalu float)
10 // 3   # 3 (floor division)
10 % 3    # 1 (modulo/sisa bagi)
2 ** 10   # 1024 (pangkat)

x = 10
x += 5      # x = x + 5
x -= 2
x *= 3
x /= 2
x //= 2
x %= 3
x **= 2

5 == 5      # True
5 != 3      # True
5 > 3       # True
5 >= 5      # True
5 < 10      # True
5 <= 5      # True
 
# Chain comparison (Pythonic)
1 < x < 10

True and False    # False
True or False     # True
not True          # False

a = [1, 2, 3]
b = a
c = [1, 2, 3]
 
a is b        # True (objek sama di memory)
a is c        # False (konten sama, objek berbeda)
a == c        # True (nilai sama)
 
1 in a        # True
4 not in a    # True
"d" in "hello"  # False

5 & 3     # 1  (AND)
5 | 3     # 7  (OR)
5 ^ 3     # 6  (XOR)
~5        # -6 (NOT)
5 << 1    # 10 (shift left)
5 >> 1    # 2  (shift right)

counter = 0
 
def increment():
    global counter
    counter += 1
 
increment()
print(counter)   # 1

True, False
 
# Truthy / Falsy
bool(0)       # False
bool("")      # False
bool([])      # False
bool(None)    # False
bool(1)       # True
bool("hi")    # True
bool([1])     # True

fruits = ["apel", "jeruk", "mangga"]
mixed = [1, "dua", 3.0, True]
 
# Akses & slice
fruits[0]          # 'apel'
fruits[-1]         # 'mangga'
fruits[1:3]        # ['jeruk', 'mangga']
 
# Mutasi
fruits.append("durian")
fruits.insert(1, "pisang")
fruits.remove("jeruk")
popped = fruits.pop()       # remove & return last
fruits.extend(["nanas", "kelapa"])
 
# Operasi
len(fruits)
"apel" in fruits           # True
sorted(fruits)             # sorted copy
fruits.sort()              # in-place sort
fruits.reverse()
 
# List comprehension
squares = [x**2 for x in range(10)]
evens = [x for x in range(20) if x % 2 == 0]

point = (3, 4)
single = (42,)          # koma penting untuk single-element
rgb = (255, 128, 0)
 
x, y = point            # unpacking
_, y = point            # ignore first
 
# Namedtuple: tuple dengan nama field
from collections import namedtuple
Point = namedtuple("Point", ["x", "y"])
p = Point(3, 4)
p.x, p.y               # 3, 4

user = {
    "name": "Alice",
    "age": 30,
    "active": True,
}
 
# Akses
user["name"]                    # 'Alice'
user.get("email", "N/A")       # 'N/A' (default jika key tidak ada)
 
# Mutasi
user["email"] = "alice@mail.com"
del user["active"]
user.pop("age")                 # remove & return
 
# Iterasi
for key, value in user.items():
    print(f"{key}: {value}")
 
user.keys()
user.values()
 
# Dict comprehension
squares = {x: x**2 for x in range(5)}
# {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
 
# Merge (Python 3.9+)
defaults = {"theme": "dark", "lang": "id"}
overrides = {"lang": "en"}
config = defaults | overrides
 
# Nested dictionary
company = {
    "name": "TechCorp",
    "employees": {
        "alice": {"role": "Engineer", "salary": 15000000},
        "bob": {"role": "Designer", "salary": 12000000},
    },
}
company["employees"]["alice"]["role"]   # 'Engineer'
 
# Copy
import copy
shallow = company.copy()
deep = copy.deepcopy(company)

colors = {"red", "green", "blue"}
nums = set([1, 2, 2, 3, 3])    # {1, 2, 3}
 
colors.add("yellow")
colors.discard("red")
 
# Operasi himpunan
a = {1, 2, 3, 4}
b = {3, 4, 5, 6}
a | b      # union: {1, 2, 3, 4, 5, 6}
a & b      # intersection: {3, 4}
a - b      # difference: {1, 2}
a ^ b      # symmetric difference: {1, 2, 5, 6}

fs = frozenset([1, 2, 3, 3])   # frozenset({1, 2, 3})
# fs.add(4)                     # AttributeError, tidak bisa diubah
 
# Berguna sebagai key dictionary atau elemen set
cache = {frozenset([1, 2]): "result_a"}

result = None
 
if result is None:
    print("Belum ada hasil")
 
# Gunakan `is` bukan `==` untuk None

int("10")        # 10
str(42)          # '42'
list("abc")      # ['a', 'b', 'c']
tuple([1, 2])    # (1, 2)
set([1, 1, 2])   # {1, 2}
dict([("a", 1), ("b", 2)])  # {'a': 1, 'b': 2}