Loops, and where your data lives
INPUT · Slides
01 / 07
To take something out by number you have to know where it is. Start with the simpler question: is it even in there?
The tool is in, the same word you used on lists. The answer comes back as True or False.
text = "heavy rain today"print("rain" in text)print("snow" in text)Result
True False
02 / 07
Since it comes back as True or False, you can write it straight into an if.
"If it contains this, do that" is now something you can express.
text = "heavy rain today"if "rain" in text: print("take an umbrella")Result
take an umbrella
03 / 07
When you want the place as well, you use find. The number where it was found comes back.
The writing is text.find("rain") — a . on the end of the string you are searching. The same shape as append on a list.
text = "heavy rain today"print(text.find("rain"))Result
6
04 / 07
find does not error when it finds nothing. It returns -1 instead.
Since a real position is never below zero, an impossible number is how it says "not there".
0 coming back means "it was right at the front", -1 means "it was not there at all". Take care not to read one for the other.
text = "heavy rain today"print(text.find("snow"))print(text.find("heavy"))Result
-1 0
05 / 07
count tells you how many times something turns up.
If there are none at all you get 0. This one never goes to -1.
word = "banana"print(word.count("a"))print(word.count("x"))Result
3 0
06 / 07
There are tools just for "does it begin with" and "does it end with".
startswith … does it begin with that stringendswith … does it end with that stringBoth answer True or False. You could slice and compare instead, but these say what they mean as you read them.
text = "heavy rain today"print(text.startswith("heavy"))print(text.endswith("tomorrow"))Result
True False
07 / 07
A number from find goes straight into a slice. The searching tools and the cutting tools are a pair.
The example below takes "from just after the : to the end". You can cut it out without knowing where the separator sits.
Next lesson is about the tools that work on a string.
line = "name:Yui"i = line.find(":")print(line[i + 1:])Result
Yui