5.4. Strings

A string is a sequence of Unicode characters written between quotes. Single quotes and double quotes are equivalent – pick the style that lets you avoid escaping the quotes that appear inside the text:

name    = "OpenMV Cam"
company = 'OpenMV, LLC'
message = "She said \"hi\""        # both styles can be used
same    = 'She said "hi"'

Triple-quoted strings ("""...""" or '''...''') span multiple lines and preserve the newlines literally:

banner = """boot ok
firmware v1.28
"""
print(banner)

Output:

boot ok
firmware v1.28

5.4.1. Escape sequences

Inside a regular string, \ introduces a special character:

• \n – newline

• \t – tab

• \\ – a literal backslash

• \' / \" – a literal quote (when it would otherwise end the string)

• \xHH – the character with hex code HH

• \uHHHH – the Unicode codepoint HHHH

When a string contains many backslashes, prefix the literal with r to make it a raw string. Backslashes are then taken literally – \n stays two characters long instead of being replaced with a newline:

win_path = r"C:\Users\OpenMV\camera.py"
literal  = r"\n is two characters, not a newline"

5.4.2. Concatenation and repetition

Two strings are joined with +; a string is repeated with *:

greeting = "Hello, " + name + "!"
line     = "-" * 40              # 40-character separator

Repeated + in a loop allocates a fresh string on every iteration. For building larger strings from many pieces, use str.join().

5.4.3. Length, indexing, and slicing

len() returns the number of characters in a string. Indexing with [] returns a one-character string at the given position; negative indices count from the end:

>>> s = "OpenMV"
>>> len(s)
6
>>> s[0]
'O'
>>> s[-1]
'V'

A slice s[start:stop] returns the substring from position start up to but not including stop. Either end can be omitted to mean “the beginning” or “the end”, and an optional third value s[start:stop:step] lets you skip characters.

Slice positions sit between characters. s[2:5] selects the characters in positions 2, 3, and 4.

>>> s = "OpenMV"
>>> s[2:5]
'enM'
>>> s[:3]
'Ope'
>>> s[3:]
'nMV'
>>> s[::-1]
'VMnepO'                     # whole string, reversed

An out-of-range slice silently returns whatever portion exists – s[100:200] is the empty string "", not an error. Indexing out of range, on the other hand, raises IndexError.

5.4.4. Immutability

Strings cannot be modified in place. Operations that look like they mutate a string actually return a new string and leave the original alone:

>>> name = "OpenMV"
>>> name.upper()
'OPENMV'
>>> name
'OpenMV'                     # unchanged

To “change” a string, rebind the name to the new value: name = name.upper().