str.split() / str.join()

# Splits a string by the delimiter and returns a list.
str.split(sep=None, maxsplit=-1)

# Splits from the right. The difference appears when maxsplit is specified.
str.rsplit(sep=None, maxsplit=-1)

# Joins each element of an iterable with the separator string and returns a string.
separator_str.join(iterable)

# Split a string with split().
sentence = "Python is fun and powerful"
words = sentence.split()  # Split on whitespace.
print(words)  # ['Python', 'is', 'fun', 'and', 'powerful']

# Split with a specific delimiter.
csv_line = "Alice,20,Tokyo,Engineer"
fields = csv_line.split(",")
print(fields)  # ['Alice', '20', 'Tokyo', 'Engineer']

# Limit the number of splits with maxsplit.
text = "a:b:c:d:e"
print(text.split(":", 2))  # ['a', 'b', 'c:d:e'] (split at most 2 times)

# Extract the filename from a path.
path = "/home/user/documents/file.txt"
parts = path.split("/")
print(parts[-1])  # file.txt (the last element is the filename)

# Split from the right with rsplit().
print(text.rsplit(":", 2))  # ['a:b:c', 'd', 'e'] (split at most 2 times from the right)

# Practical example: separate a file extension.
filename = "photo.2026.jpg"
name, ext = filename.rsplit(".", 1)  # Split only once from the right.
print(name)  # photo.2026
print(ext)   # jpg

# Use join() to combine a list into a string.
words2 = ["Python", "is", "fun"]
result = " ".join(words2)  # Join with a space.
print(result)  # Python is fun

# Build a CSV line.
data = ["Alice", "25", "Osaka"]
csv = ",".join(data)
print(csv)  # Alice,25,Osaka

# Join lines with newlines to build a block of text.
lines = ["Line 1", "Line 2", "Line 3"]
text = "\n".join(lines)
print(text)
# Line 1
# Line 2
# Line 3

# join() requires all elements to be strings. Convert numbers first.
nums = [1, 2, 3, 4, 5]
print("-".join(str(n) for n in nums))  # 1-2-3-4-5

# Normalize whitespace by combining split() and join().
messy = "  Python   is   fun  "
normalized = " ".join(messy.split())
print(normalized)  # Python is fun

When the argument to split() is omitted (or set to None), consecutive whitespace characters are treated as a single delimiter, and leading and trailing whitespace is also removed. Passing an empty string as the delimiter raises a ValueError.

With join(), it is Python convention to write the separator first. This may feel counterintuitive at first, but it has advantages — for example, you can concatenate elements with no separator by writing "".join(parts). All elements passed to join() must be strings. If the iterable contains integers or other non-string types, a TypeError is raised, so convert them with str() beforehand.

For string replacement, see str.replace(). For trimming whitespace, see str.strip().