Python string list deduplication

Weight to a relatively high frequency strings, and lists recent interview 
pstr = 'abcadcf' 
# deduplication string 
# 1, using the set - is not maintained in the original sequence

print(set(pstr))

# 2, using a dictionary - did not keep the original order

print({}.fromkeys(pstr).keys())

# 3, using a loop through method - the code is simple enough, not high-end

a = []
for i in range(len(pstr)):
    if pstr[i] not in a:
        a.append(pstr[i])
print(a)

# List deduplication

plist = [1,0,3,7,5,7]

# 1, using the set method

print(list(set(plist)))

# 2, use the dictionary

print(list({}.fromkeys(plist).keys()))

# 3, loop through Law

plist1 = []
for i in plist:
    if i not in plist1:
        plist1.append(i)
print(plist1)

# 4, according to the index ordering again

b = list(set(plist))
b.sort(key=plist.index)
print('sds:',b)