1a = "hello"
2b = "hello"
3
4# Value equality — checks if contents are the same
5print(a == b)  # True
6
7# Identity — checks if they are the exact same object in memory
8print(a is b)  # True (due to string interning — but DON'T rely on this!)

1a = "hello world"
2b = "hello" + " " + "world"
3
4print(a == b)   # True — same content
5print(a is b)   # False — different objects in memory
6
7# Another example
8a = "hello!"
9b = "hello!"
10print(a == b)   # True
11print(a is b)   # False (may be True in some Python implementations, not guaranteed)

1# Short strings that look like identifiers are interned
2a = "hello"
3b = "hello"
4print(a is b)  # True — Python reuses the same object
5
6# Strings with spaces, punctuation, or special characters are NOT always interned
7a = "hello world"
8b = "hello world"
9print(a is b)  # May be True or False — implementation-dependent!
10
11# Compile-time constants may be interned
12a = "hello" + "world"  # Computed at compile time
13b = "helloworld"
14print(a is b)  # True in CPython — both are compile-time constants
15
16# Runtime-computed strings are NOT interned
17x = "world"
18a = "hello" + x  # Computed at runtime
19b = "helloworld"
20print(a is b)  # False

1# CORRECT: Use == for string comparison
2username = get_username()
3if username == "admin":
4    grant_access()
5
6# CORRECT: Use is for None checks
7result = find_user("alice")
8if result is None:
9    print("User not found")
10
11# WRONG: Using is for string comparison
12if username is "admin":  # Unreliable!
13    grant_access()

1a = "hello"
2b = "hello"
3print(id(a))       # 140234567890 (example address)
4print(id(b))       # 140234567890 (same — interned)
5print(a is b)      # True
6print(id(a) == id(b))  # True
7
8c = "hello world"
9d = "hello world"
10print(id(c))       # 140234567990
11print(id(d))       # 140234568090 (different — not interned)
12print(c is d)      # False

1import sys
2
3# Intern strings for fast identity comparison
4a = sys.intern("hello world")
5b = sys.intern("hello world")
6print(a is b)  # True — both point to the same interned string
7
8# Use case: dictionary keys in a large dataset
9# Interning reduces memory and speeds up key lookups
10keys = [sys.intern(key) for key in raw_keys]

1# Case-insensitive comparison
2if name.lower() == "admin":
3    print("Welcome, admin")
4
5# Prefix/suffix checking
6if filename.startswith("."):
7    print("Hidden file")
8if filename.endswith(".py"):
9    print("Python file")
10
11# Substring check
12if "error" in log_line:
13    print("Error found")
14
15# Compare with multiple values
16if status in ("active", "pending", "trial"):
17    allow_access()

1# Pylint: W0123 (comparison-with-callable)
2# Flake8: E711 (comparison to None)
3
4if name is "admin":  # SyntaxWarning in Python 3.8+
5    pass
6# SyntaxWarning: "is" with a literal. Did you mean "=="?