Python ord, chr Built InsUse the ord and chr built-in methods. These convert characters to integers and back again.
Think of letters like A, B and C. These are parts of words. But they have an underlying representation. A sequence of bits that represents that letter.Strings
In Python characters are represented by numbers. Often we use a one-character string. With ord we convert this into an integer. With chr, an integer into a string.Built-ins
In this program, each "letter" is a one-character string. We call ord and the result in an integer. We can do things like multiply or add that integer.
Note: The letters A, B and C have sequential numbers. This is how they are stored in ASCII.
Note 2: The number strings 1, 2 and 3 are made of characters that are represented in ASCII by 49, 50 and 51.
Python program that uses ord built-in
letters = "ABCabc123"
for letter in letters:
# Get number that represents letter in ASCII.
number = ord(letter)
print(letter, "=", number)
A = 65
B = 66
C = 67
a = 97
b = 98
c = 99
1 = 49
2 = 50
3 = 51
Next we consider the chr built-in function. This does the opposite of ord. It converts a number (an integer) into a one-character string.
Here: We convert 97 back into the lowercase "a." This code could be used to round-trip letters and digits.
Python program that uses chr
numbers = [97, 98, 99]
for number in numbers:
# Convert ASCII-based number to character.
letter = chr(number)
print(number, "=", letter)
97 = a
98 = b
99 = c
Let's do something really crazy. Here we create strings with chr in for-loops for use as the mapped keys and values of maketrans. We then translate the strings.
So: We generate translation keys and values with an algorithm, and then apply the generated table to translate strings.
Python program that uses chr, maketrans, translate
# Generate string for translation.
initial = ""
for i in range(97, 97 + 26):
initial += chr(i)
# Generate mapped chars for string.
translated = ""
for i in range(97, 97 + 26):
translated += chr(i - 10)
print("INITIAL ", initial)
# Create a lookup table.
table = str.maketrans(initial, translated)
# Translate this string.
value = "thank you for visiting"
result = value.translate(table)
print("AFTER ", result)
BEFORE thank you for visiting
AFTER j^Wda oek \eh l_i_j_d]
The simplest examples above would not be found in real programs. But algorithms like ROT13, which are used sometimes in programs, also can be implemented with ord and chr.
Also: Ord and chr built-ins help transform characters and strings. But they are not ideal for all translations.ROT13
Translate: With maketrans and translate() we can translate strings. We can use chr and ord to build translation strings for these methods.Translate
A summary. Chr and ord are something we need to know to effectively use Python. There is a difference between an integer and a one-character string.
We must convert to an integer with ord—and back to a string with chr. We can change characters by adding or subtracting offset values.
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