String Built-in Functions

Python strings have many useful built-in methods (all return a new string/value — strings are immutable).

count() and find()

s = "banana"
print(s.count("a"))         # 3
print(s.find("na"))         # 2 (index of first occurrence)
print(s.find("xyz"))        # -1 (not found)

capitalize(), title(), lower(), upper(), swapcase()

s = "python PROGRAMMING language"
print(s.capitalize())   # 'Python programming language'
print(s.title())        # 'Python Programming Language'
print(s.lower())        # 'python programming language'
print(s.upper())        # 'PYTHON PROGRAMMING LANGUAGE'
print(s.swapcase())     # 'PYTHON programming LANGUAGE'

replace()

s = "I like Java"
print(s.replace("Java", "Python"))   # 'I like Python'

join()

Joins elements of an iterable into a single string, using the calling string as separator.

words = ["Python", "is", "fun"]
print(" ".join(words))      # 'Python is fun'
print("-".join(words))      # 'Python-is-fun'
print("".join(["H","i"]))   # 'Hi'

isspace(), isdigit()

print("   ".isspace())    # True
print("abc".isspace())    # False
print("12345".isdigit())  # True
print("12a45".isdigit())  # False

split()

Breaks a string into a list, using whitespace (or a given separator) as delimiter.

s = "Python is fun"
print(s.split())          # ['Python', 'is', 'fun']

csv = "Riya,21,BCA"
print(csv.split(","))     # ['Riya', '21', 'BCA']

startswith() and endswith()

s = "hello.py"
print(s.startswith("hello"))   # True
print(s.endswith(".py"))       # True
print(s.endswith(".txt"))      # False

Quick reference table

Combined example — word frequency

sentence = "python is easy python is fun"
words = sentence.split()
freq = {}
for w in words:
    freq[w] = freq.get(w, 0) + 1
print(freq)   # {'python': 2, 'is': 2, 'easy': 1, 'fun': 1}