370 lines
7.9 KiB
Markdown
370 lines
7.9 KiB
Markdown
# Sequence Types: list
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{:.no_toc}
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<nav markdown="1" class="toc-class">
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* TOC
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{:toc}
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</nav>
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## The goal
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> Lists are **mutable** sequences, **typically** used to store collections of **homogeneous** items (where the precise degree of similarity will vary by application).
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[Quote](https://docs.python.org/3/library/stdtypes.html#lists)
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Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
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## Example Lists
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With homogeneous items:
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```python
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primes = [2, 3, 5, 7]
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collection_of_strings = [
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"AA",
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"BB",
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"CC",
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"DD",
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"EE",
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"FF",
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"GG",
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"HH",
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]
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```
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A mixture of type:
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```python
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def my_function(a):
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return a
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my_favourite_things = [32, "sleep", my_function]
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```
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## Indexing
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```python
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collection_of_strings = [
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"AA",
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"BB",
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"CC",
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"DD",
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"EE",
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"FF",
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"GG",
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"HH",
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]
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print(collection_of_strings[0]) # -> AA
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print(collection_of_strings[1]) # -> BB
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print(collection_of_strings[-2]) # -> GG
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print(collection_of_strings[-1]) # -> HH
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```
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## Slicing
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```python
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collection_of_strings = [
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"AA",
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"BB",
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"CC",
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"DD",
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"EE",
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"FF",
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"GG",
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"HH",
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]
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print(collection_of_strings[0:3]) # -> ['AA', 'BB', 'CC']
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print(collection_of_strings[:3]) # -> ['AA', 'BB', 'CC']
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print(collection_of_strings[3:]) # -> ['DD', 'EE', 'FF', 'GG', 'HH']
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print(collection_of_strings[1:-1]) # -> ['BB', 'CC', 'DD', 'EE', 'FF', 'GG']
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print(collection_of_strings[-3:]) # -> ['FF', 'GG', 'HH']
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print(collection_of_strings[0:3]) # -> ['AA', 'BB', 'CC']
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print(collection_of_strings[0:3:1]) # -> ['AA', 'BB', 'CC']
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print(collection_of_strings[0:3:2]) # -> ['AA', 'CC']
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print(collection_of_strings[::2]) # -> ['AA', 'CC', 'EE', 'GG']
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```
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## Changing lists
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```python
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collection_of_strings = [
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"AA",
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"BB",
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"CC",
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"DD",
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"EE",
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"FF",
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"GG",
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"HH",
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]
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collection_of_strings[3] = "II"
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print(collection_of_strings) # -> ['AA', 'BB', 'CC', 'II', 'EE', 'FF', 'GG', 'HH']
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collection_of_strings[:3] = ["JJ", "KK", "LL"]
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print(collection_of_strings) # -> ['JJ', 'KK', 'LL', 'II', 'EE', 'FF', 'GG', 'HH']
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collection_of_strings[:4] = [
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"MM",
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"NN",
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"OO",
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"PP",
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]
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print(collection_of_strings) # -> ['MM', 'NN', 'OO', 'PP', 'EE', 'FF', 'GG', 'HH']
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```
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## List functions
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### [len()](https://docs.python.org/3/library/functions.html#len) and [sorted()](https://docs.python.org/3/library/functions.html#sorted)
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```python
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collection_of_strings = [
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"GG",
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"HH",
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"AA",
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"BB",
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"EE",
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"FF",
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"CC",
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"DD",
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]
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print(len(collection_of_strings)) # -> 8
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print(sorted(collection_of_strings)) # -> ['AA', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH']
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```
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### [max()](https://docs.python.org/3/library/functions.html#max), [min](https://docs.python.org/3/library/functions.html#min) and [sum()](https://docs.python.org/3/library/functions.html#sum)
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```python
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primes = [2, 3, 5, 7]
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print(sum(primes)) # -> 17
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print(max(primes)) # -> 7
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print(min(primes)) # -> 2
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```
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## in
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Is **x in list**?
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```python
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collection_of_strings = [
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"AA",
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"BB",
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"CC",
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"DD",
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"EE",
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"FF",
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"GG",
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"HH",
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]
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print("AA" in collection_of_strings) # -> True
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print("XX" in collection_of_strings) # -> False
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print("AA" not in collection_of_strings) # -> False
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print("XX" not in collection_of_strings) # -> True
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```
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## [Index](https://docs.python.org/3/tutorial/datastructures.html#more-on-lists)
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Which index id has an element in a list?
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```python
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collection_of_strings = [
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"AA",
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"BB",
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"CC",
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"DD",
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"EE",
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"FF",
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"GG",
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"HH",
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]
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print(collection_of_strings.index("CC")) # -> 2
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print(collection_of_strings.index("XX")) # -> ValueError: 'XX' is not in list
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```
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Maybe we don't want to start in the beginning of the list or don't want to search until the end of the list:
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```python
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collection_of_strings = [
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"AA",
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"BB",
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"CC",
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"DD",
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"EE",
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"BB",
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"FF",
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"GG",
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"BB",
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"HH",
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]
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print(collection_of_strings.index("BB")) # -> 1
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# At or after 2
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print(collection_of_strings.index("BB", 2)) # -> 5
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# Before 6
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print(collection_of_strings.index("BB", 2, 6)) # -> 5
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# Before 4
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print(collection_of_strings.index("BB", 2, 4)) # ValueError: 'BB' is not in list
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```
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### [append()](https://docs.python.org/3/tutorial/datastructures.html#more-on-lists), [pop()](https://docs.python.org/3/tutorial/datastructures.html#more-on-lists), and [remove()](https://docs.python.org/3/tutorial/datastructures.html#more-on-lists)
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```python
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collection_of_strings = [
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"AA",
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"BB",
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"BB",
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"CC",
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"DD",
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"EE",
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"FF",
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"GG",
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"HH",
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]
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collection_of_strings.append("II")
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print(
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collection_of_strings
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) # -> ['AA', 'BB', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH', 'II']
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print(collection_of_strings.pop()) # -> II
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print(
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collection_of_strings
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) # -> ['AA', 'BB', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH']
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collection_of_strings.remove("BB")
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print(collection_of_strings) # -> ['AA', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH']
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collection_of_strings.remove("BB")
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print(collection_of_strings) # -> ['AA', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH']
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collection_of_strings.remove("BB")
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print(collection_of_strings) # -> ValueError: list.remove(x): x not in list
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```
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## [del](https://docs.python.org/3/tutorial/datastructures.html#the-del-statement) and [insert()](https://docs.python.org/3/tutorial/datastructures.html#more-on-lists)
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Insert and delete an element.
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```python
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collection_of_strings = []
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collection_of_strings.append("BB")
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collection_of_strings.append("CC")
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collection_of_strings.append("DD")
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print(collection_of_strings) # -> ['BB', 'CC', 'DD']
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collection_of_strings.insert(0, "AA")
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print(collection_of_strings) # -> ['AA', 'BB', 'CC', 'DD']
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del collection_of_strings[1]
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print(collection_of_strings) # -> ['AA', 'CC', 'DD']
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```
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## +
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Concatenating lists.
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```python
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collection_of_strings_a = [
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"AA",
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"BB",
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"CC",
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"DD",
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]
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collection_of_strings_b = [
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"EE",
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"FF",
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"GG",
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"HH",
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]
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print(collection_of_strings_a) # -> ['AA', 'BB', 'CC', 'DD']
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print(collection_of_strings_b) # -> ['EE', 'FF', 'GG', 'HH']
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collection_of_strings = collection_of_strings_a + collection_of_strings_b
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print(collection_of_strings) # -> ['AA', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH']
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```
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## *
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Repeat a list several times.
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```python
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collection_of_strings = [
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"AA",
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"BB",
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"CC",
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]
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print(3 * collection_of_strings) # -> ['AA', 'BB', 'CC', 'AA', 'BB', 'CC', 'AA', 'BB', 'CC']
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print(collection_of_strings * 3) # -> ['AA', 'BB', 'CC', 'AA', 'BB', 'CC', 'AA', 'BB', 'CC']
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```
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## count()
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How often does an element occur in the list?
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```python
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collection_of_strings = [
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"AA",
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"AA",
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"BB",
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"BB",
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"BB",
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"CC",
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"DD",
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"EE",
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"FF",
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"GG",
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"HH",
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]
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print(collection_of_strings.count("AA")) # -> 2
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print(collection_of_strings.count("BB")) # -> 3
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print(collection_of_strings.count("CC")) # -> 1
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```
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## [Additional commands](https://docs.python.org/3/tutorial/datastructures.html)
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|---|
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|list.append(x)|
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|list.extend(iterable)|
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|list.insert(i, x)|
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|list.remove(x)|
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|list.pop([i])|
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|list.clear()|
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|list.index(x[, start[, end]])|
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|list.count(x)|
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|list.sort(*, key=None, reverse=False)|
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|list.reverse()|
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|list.copy()|
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## [Common Sequence Operations](https://docs.python.org/3/library/stdtypes.html#sequence-types-list-tuple-range)
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|Operation|Result|
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|x in s|True if an item of s is equal to x, else False|
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|x not in s|False if an item of s is equal to x, else True|
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|s + t|the concatenation of s and t|
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|s * n or n * s|equivalent to adding s to itself n times|
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|s[i]|ith item of s, origin 0|
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|s[i:j]|slice of s from i to j|
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|s[i:j:k]|slice of s from i to j with step k|
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|len(s)|length of s|
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|min(s)|smallest item of s|
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|max(s)|largest item of s|
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|s.index(x[, i[, j]])|index of the first occurrence of x in s (at or after index i and before index j)|
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|s.count(x)|total number of occurrences of x in s|
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