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data = ["John", "Doe", "was", "here"]
Don't do it like this. While loops are actually really rarely needed.
idx = 0
while idx < len(data):
print(data[idx])
idx += 1
John Doe was here
Don't do like this either.
for idx in range(len(data)):
print(data[idx])
John Doe was here
for item in data:
print(item)
John Doe was here
If you need the index as well, you can use enumerate.
for idx, val in enumerate(data):
print(f"{idx}: {val}")
0: John 1: Doe 2: was 3: here
Don't do this.
i = 0
while i < 6:
print(i)
i += 1
0 1 2 3 4 5
Don't do this either.
for val in [0, 1, 2, 3, 4, 5]:
print(val)
0 1 2 3 4 5
for val in range(6):
print(val)
0 1 2 3 4 5
data = ["first", "to", "last", "from"]
This is no good.
i = len(data) - 1
while i >= 0:
print(data[i])
i -= 1
from last to first
for item in reversed(data):
print(item)
from last to first
collection1 = ["a", "b", "c"]
collection2 = (10, 20, 30, 40, 50)
collection3 = ["John", "Doe", True]
Oh boy, not like this.
shortest = len(collection1)
if len(collection2) < shortest:
shortest = len(collection2)
if len(collection3) < shortest:
shortest = len(collection3)
i = 0
while i < shortest:
print(collection1[i], collection2[i], collection3[i])
i += 1
a 10 John b 20 Doe c 30 True
This is getting better but there's even a better way!
shortest = min(len(collection1), len(collection2), len(collection3))
for i in range(shortest):
print(collection1[i], collection2[i], collection3[i])
a 10 John b 20 Doe c 30 True
for first, second, third in zip(collection1, collection2, collection3):
print(first, second, third)
a 10 John b 20 Doe c 30 True
You can also create a dict out of two collections!
my_dict = dict(zip(collection1, collection2))
print(my_dict)
{'a': 10, 'b': 20, 'c': 30}
for - else - Checking for a match in a collection¶Let's say we want to verify a certain condition is met by at least one element in a collection. Let's consider the following relatively naive example where we want to verify that at least one item is "python" (case insensitive) in data. If not, we'll raise a ValueError.
data = [1, 2, 3, "This", "is", "just", "a", "random", "Python", "list"]
Don't do it like this
found = False
for val in data:
if str(val).lower() == "python":
found = True
break
if not found:
raise ValueError("Nope, couldn't find.")
for val in data:
if str(val).lower() == "python":
break
else:
raise ValueError("Nope, couldn't find.")