How map() works
map() takes a function and one or more iterables. It applies the function to each item and returns a map object, a lazy iterator.
map(function, iterable1, iterable2, ...)When you use several iterables, map() stops at the shortest one.
Convert a map object to a list
A map object does not show its values by itself. Convert it with list().
Example: square each item.
nums = [11, 22, 33, 44, 55]
squares = map(lambda x: x ** 2, nums)
convList = list(squares)
print(convList)
Output:
[121, 484, 1089, 1936, 3025]Use map() with several iterables
inputList1 = [11, 22, 33]
inputList2 = [44, 55, 66]
resultList = map(lambda x, y: x + y, inputList1, inputList2)
print(list(resultList))
Output:
[55, 77, 99]Get the first character of each string
employees = ['Anna', 'Omar', 'Karim', 'David']
firstLetters = map(lambda s: s[0], employees)
extractedChars = list(firstLetters)
print(extractedChars)
Output:
['A', 'O', 'K', 'D']Change letter case
names = ['anna', 'omar', 'karim']
upperNames = map(str.upper, names)
print(list(upperNames))
Output:
['ANNA', 'OMAR', 'KARIM']You can pass a built-in function like str.upper directly.
Convert Celsius to Fahrenheit
def to_fahrenheit(c):
return (c * 9 / 5) + 32
celsius = [0, 20, 37, 100]
fahrenheit = map(to_fahrenheit, celsius)
print(list(fahrenheit))
Output:
[32.0, 68.0, 98.6, 212.0]map() or a list comprehension
A list comprehension often reads better:
squares = [x ** 2 for x in nums]Use map() when you already have a named function, or when you want a lazy iterator that does not build the whole list at once.
Quick recap
map(func, iterable)returns a lazy iterator, so wrap it inlist()to see values.