Python · Strings: indexing, slicing, methods

A string is an immutable sequence of Unicode characters. Immutable means s[0] = "X" raises an error, and every “changing” method actually returns a new string.

Indexing starts at 0. Negative indexes count from the end, so s[-1] is the last character.

Slicing is s[start:stop:step]. start is included and stop is excluded, and any of the three can be left out. s[::-1] reverses a string.

The methods I’ll use most:

method	does
strip()	removes whitespace at both ends
lower() / upper()	changes case
split(sep)	turns a string into a list of parts
"sep".join(list)	the reverse of split
replace(a, b)	returns a copy with replacements
find(x) / in	searches

s = "  Pandit Deendayal Energy University  "
t = s.strip()
print(repr(t))
print(t[0], t[-1], t[7:16], t[::-1][:10])

words = t.split()
print(words, len(words))
print("".join(w[0] for w in words))   # initials
print(t.lower().replace("university", "Univ."))
print("Energy" in t, t.find("Energy"))

try:
    t[0] = "p"
except TypeError as e:
    print("TypeError:", e)

Output:

'Pandit Deendayal Energy University'
P y Deendayal ytisrevinU
['Pandit', 'Deendayal', 'Energy', 'University'] 4
PDEU
pandit deendayal energy Univ.
True 17
TypeError: 'str' object does not support item assignment