Summary of how to use Python list

Introduction

This is a summary for those who have studied once, but "What was this? How was this ...".

Python can now be selected in FE (Fundamental Information Technology Engineer Examination). Originally, this spring exam was scheduled to be the first question, but it was canceled due to the influence of Corona.

Such a Python list is also given in the FE example, so I tried to summarize how to use it.

You can look back just before the exam, or remember the methods that you tend to forget in everyday programming. Please use all means.

Initialize list

First of all, from the basic list declaration.

alist = []
blist = [1, 1, 2, 3, 5, 8, 13]
clist = list(range(5))
dlist = [i for i in range(10) if (i % 2 == 0)]  #List comprehension

print(f"alist = {alist}\nblist = {blist}\nclist = {clist}\ndlist = {dlist}")

output

alist = []
blist = [1, 1, 2, 3, 5, 8, 13]
clist = [0, 1, 2, 3, 4]
dlist = [0, 2, 4, 6, 8]

Substitution and copy

It's a blind spot. Therefore, in the following handling of list, both passing by reference and passing by value will be explained.

--Substitute list with = --Pass by reference --The assignment source (ʻalist) changes → blistalso changes --Substitute the return value of the.copy () method --Pass by value --The assignment source (ʻalist) has changed → clist has not changed

alist = [1, 2, 3]

#Pass by reference
blist = alist

#Pass by value
clist = alist.copy()

def delete_middle(list_obj, msg):
    list_obj.pop(int(len(list_obj)/2))
    print(msg, list_obj)
    
delete_middle(alist, "alist =")
print(f"blist = {blist}")
print(f"clist = {clist}")

output

alist = [1, 3]
blist = [1, 3]
clist = [1, 2, 3]

Add element to list

--Add only one element to the end --. Append (x) method --Add one to the specified index location --. Insert (index, obj) method --Add list to list --Use + operator --Even if the elements of blist and clist change after the operation, it does not affect dlist.

alist = [1, 2, 3]
blist = alist
clist = alist.copy()

#Add 4 to the back
alist.append(4)

#Add 100 to index of 1
alist.insert(1, 100)

#Add list to list
dlist = blist + clist

print(f"alist = {alist}\nblist = {blist}\nclist = {clist}\ndlist = {dlist}")

alist = [1, 100, 2, 3, 4]
blist = [1, 100, 2, 3, 4]
clist = [1, 2, 3]
dlist = [1, 100, 2, 3, 4, 1, 2, 3]

Delete the contents of list

Delete by specifying index

alist = [1, 3, 5, 7, 9]
blist = alist
clist = alist.copy()

del alist[2]
print(f"del alist[2] =>\n\talist = {alist}\n\tblist = {blist}\n\tclist = {clist}\n")

alist.pop(2)
print(f"alist.pop(2) =>\n\talist = {alist}\n\tblist = {blist}\n\tclist = {clist}")

output

del alist[2] =>
	alist = [1, 3, 7, 9]
	blist = [1, 3, 7, 9]
	clist = [1, 3, 5, 7, 9]

alist.pop(2) =>
	alist = [1, 3, 9]
	blist = [1, 3, 9]
	clist = [1, 3, 5, 7, 9]

Delete by specifying a value

Only the value at the beginning is deleted. Not all of its values.

alist = [1, 2, 2, 3, 3, 3]
blist = alist
clist = alist.copy()

alist.remove(2)

print(f"alist = {alist}\nblist = {blist}\nclist = {clist}")

output

alist = [1, 2, 3, 3, 3]
blist = [1, 2, 3, 3, 3]
clist = [1, 2, 2, 3, 3, 3]

Delete the last item

If you do not put an argument in .pop (), it is the same as .pop (-1), and the last element of the list is deleted.

alist = [1, 3, 5, 7, 9]
blist = alist
clist = alist.copy()

alist.pop()
print(f"alist.pop(2) =>\n\talist = {alist}\n\tblist = {blist}\n\tclist = {clist}")

output

alist.pop() =>
	alist = [1, 3, 5, 7]
	blist = [1, 3, 5, 7]
	clist = [1, 3, 5, 7, 9]

Delete all

alist = [1, 2, 3]
blist = alist
clist = alist.copy()

# alist = []The same thing is done.
# alist = []It's confusing with the declaration, but it's the development team's preference.
alist.clear()

print(f"alist = {alist}\nblist = {blist}\nclist = {clist}")

output

alist = []
blist = []
clist = [1, 2, 3]

Sort by value

alist = [20, 1, 5, 13, 8]
blist = alist
clist = alist.copy()

alist.sort()

print(f"alist = {alist}\nblist = {blist}\nclist = {clist}")

output

alist = [1, 5, 8, 13, 20]
blist = [1, 5, 8, 13, 20]
clist = [20, 1, 5, 13, 8]

Examine the index of the first value to appear

alist = [333, 1, 333, 22, 333, 22]
#22 is in what order
index = alist.index(22)
print(f"index = {index}")

output

index = 3

How many values are included

alist = [0, 1, 1, 0, 1, 0 ,1, 0, 0]
#How many times 1 came out
count = alist.count(1)
print(f"count = {count}")

output

count = 4

at the end

I think that the list method of the major is suppressed. I wanted to explain the behavior of passing by reference and passing by value, so it became difficult to read. Excuse me mm

I hope you can use it as a memorandum. Well then.