Convert a List of Strings and a List of Numbers to Each Other in Python
This article explains how to convert a list of strings (str) and a list of numbers (int, float) to each other in Python.
List comprehensions, which are useful for creating new lists from existing ones, are used in the sample code in this article. See the following article for details about list comprehensions.
See the following article for more details on converting strings to numbers.
Convert a list of numbers (int, float) to a list of strings (str)
Convert numbers to decimal strings
The str() function is used to convert numbers into decimal strings.
l_n = [-0.5, 0, 1.0, 100, 1.2e-2, 0xff, 0b11]
l_n_str = [str(n) for n in l_n]
print(l_n_str)
# ['-0.5', '0', '1.0', '100', '0.012', '255', '3']
Note that numbers may be automatically expressed in exponential notation depending on the number of digits.
Convert numbers to binary, octal, and hexadecimal strings
To convert numbers into binary, octal, or hexadecimal strings, use bin(), oct(), hex(), or format().
l_i = [0, 64, 128, 192, 256]
l_i_hex1 = [hex(i) for i in l_i]
print(l_i_hex1)
# ['0x0', '0x40', '0x80', '0xc0', '0x100']
l_i_hex2 = [format(i, '04x') for i in l_i]
print(l_i_hex2)
# ['0000', '0040', '0080', '00c0', '0100']
l_i_hex3 = [format(i, '#06x') for i in l_i]
print(l_i_hex3)
# ['0x0000', '0x0040', '0x0080', '0x00c0', '0x0100']
Convert numbers to exponential strings
As previously mentioned, some numbers might be automatically represented in exponential notation, depending on their digit count. The format() function allows explicit conversion into exponential strings.
For details about format() and str.format(), including format specification strings, see the following article.
If you specify E instead of e as an argument, the output string will also include E.
l_f = [0.0001, 123.456, 123400000]
l_f_e1 = [format(f, 'e') for f in l_f]
print(l_f_e1)
# ['1.000000e-04', '1.234560e+02', '1.234000e+08']
l_f_e2 = [format(f, '.3E') for f in l_f]
print(l_f_e2)
# ['1.000E-04', '1.235E+02', '1.234E+08']
Convert a list of strings (str) to a list of numbers (int, float)
Convert decimal strings to numbers
Use int() or float() to convert a string to a number.
l_si = ['-10', '0', '100']
l_si_i = [int(s) for s in l_si]
print(l_si_i)
# [-10, 0, 100]
l_sf = ['.123', '1.23', '123']
l_sf_f = [float(s) for s in l_sf]
print(l_sf_f)
# [0.123, 1.23, 123.0]
Convert binary, octal, and hexadecimal strings to numbers
The int() function accepts a radix as a second argument. It treats strings as binary, octal, or hexadecimal numbers if the second argument is 2, 8, or 16.
If 0 is passed as the second argument to int(), strings prefixed with 0b, 0o or 0x (0B, 0O or 0X) are recognized as binary, octal, or hexadecimal numbers.
l_sb = ['0011', '0101', '1111']
l_sb_i = [int(s, 2) for s in l_sb]
print(l_sb_i)
# [3, 5, 15]
l_sbox = ['100', '0b100', '0o77', '0xff']
l_sbox_i = [int(s, 0) for s in l_sbox]
print(l_sbox_i)
# [100, 4, 63, 255]
Convert exponential strings to numbers
Strings in exponential notation can be converted directly with float().
l_se = ['1.23e3', '0.123e-1', '123']
l_se_f = [float(s) for s in l_se]
print(l_se_f)
# [1230.0, 0.0123, 123.0]
Convert only convertible strings to numbers
Attempting to convert a non-convertible string into a number with int() or float() throws a ValueError. To prevent this, define a function that returns False when an error occurs. This way, only convertible elements will be converted into numbers.
def is_int(s):
try:
int(s)
except ValueError:
return False
else:
return True
def is_float(s):
try:
float(s)
except ValueError:
return False
else:
return True
l_multi = ['-100', '100', '1.23', '1.23e2', 'one']
l_multi_i = [int(s) for s in l_multi if is_int(s)]
print(l_multi_i)
# [-100, 100]
l_multi_f = [float(s) for s in l_multi if is_float(s)]
print(l_multi_f)
# [-100.0, 100.0, 1.23, 123.0]
Refer to the following article for more on exception handling.