Master Python’s Built‑In Functions: From range to zip

Functions are organized, reusable code blocks that perform a single or related task. Python provides many built‑in functions, which this article introduces.

1. range() function

Creates an immutable sequence of numbers. It takes up to three integer arguments: start (default 0), stop, and step (default 1).

Example: range(4) yields [0, 1, 2, 3]; range(1, 10, 2) yields [1, 3, 5, 7, 9].

print(list(range(4)))  # [0, 1, 2, 3]
print(list(range(1, 10, 2)))  # [1, 3, 5, 7, 9]

range can be used with a for loop to repeat an operation.

for i in range(3):
    print("Hello!")

2. Common mathematical functions

abs(x)

: returns the absolute value. divmod(a, b): returns a tuple (quotient, remainder). round(x): rounds to the nearest integer. pow(a, b, mod=None): computes a**b, optionally modulo mod. sum(iterable): returns the sum of elements. min(...) and max(...): return the smallest or largest value.

print(abs(-5))          # 5
print(divmod(13, 2))    # (6, 1)
print(round(3.5))        # 4
print(pow(5, 2, 3))     # 1
print(sum([1,2,3,4,5,6,7,8,9,10]))  # 55
print(min(3,2,5,19,6,3)) # 2
print(max(3,5,12,8,5,11)) # 12

3. Base‑conversion functions

bin(x)

: returns binary string prefixed with “0b”. oct(x): returns octal string prefixed with “0o”. hex(x): returns hexadecimal string prefixed with “0x”.

print(bin(10))   # 0b1010
print(hex(10))   # 0xa
print(oct(10))   # 0o12

4. String‑related functions

lower()

: converts all characters to lowercase. upper(): converts all characters to uppercase. count(sub, start=0, end=None): counts occurrences of sub. startswith(prefix) / endswith(suffix): test string boundaries. find(sub, start=0, end=None): returns index or -1. index(sub): like find but raises ValueError if not found. replace(old, new, count=-1): replaces occurrences. strip(chars=None): removes leading/trailing whitespace or specified chars.

str1 = "aaBBccEEff"
print(str1.lower())   # aabbcceeff
print(str1.upper())   # AABBCCEEFF

s = "aabbaaccdddb"
print(s.count("a"))          # 4
print(s.count("a", 3))       # 2
print(s.count("a", 0, 3))    # 2

s2 = "abcd"
print(s2.startswith("a"))    # True
print(s2.endswith("d"))      # True

print(s2.find("b"))         # 1
print(s2.index("c"))        # 2

print(s2.replace("a","W"))  # WbcdWbcdWbcd
print("  abc  ".strip())     # abc
print("xxyyyzzzx".strip("x")) # yyyzzz

5. Iterable‑related functions

len(obj)

: returns number of items. sort() / sorted(iterable, reverse=False): sort items. zip(*iterables): aggregates elements from each iterable into tuples. filter(func, iterable): yields items where func(item) is true. map(func, iterable): applies func to each item.

lst = [5,7,6,12,1,13,9,18,5]
lst.sort()
print(lst)  # [1,5,5,6,7,9,12,13,18]

print(sorted(lst, reverse=True))  # [18,13,12,9,7,6,5,5,1]

a = ['a','b','c']
b = ['1','2','3']
c = ['one','two','three']
for item in zip(a, b, c):
    print(item)  # ('a','1','one') ...

def is_odd(i):
    return i % 2 == 1
print(list(filter(is_odd, range(1,10))))  # [1,3,5,7,9]

def identity(i):
    return i
print(list(map(identity, [1,2,3])))  # [1,2,3]