So many collections can be iterated, like ordered collections: list, tuple, str, and unicode; unordered collections: set and dict
Iteration with index
enumerate(), this method can bind index and name at the same time, each element is not the one which existed, after binding the index, it will become a tuple which contains index and name
example
List: L = ['Bin', 100, True]
enumerate(L) = [(0, 'Bin'), (1, 100), (2, True)]
//Code==========
for index, name in enumerate(L):
print index, '-', name
//Result==========
0 - Bin
1 - 100
2 - True
By using
zip()we can easily inplement theenumerate(),
numList=range(3)=>[0, 1, 2]
zip( numList , ['Bin', 100, True] )=>[(0, 'Bin'), (1, 100), (2, True)]
Iteration of dict
========== Python3 ==========
dict.items(): return a list of entities, each entity is a tuple which contains a key and a value
dict.keys(): return a list of keys
dict.values(): return a list of values
example
//Code==========
dict = {'Name': 'Bin', 'Age': 3}
for i,j in dict.items():
print(i, ":", j)
//Result==========
Name : Bin
Age : 3
========== Python2 ==========
dict.values(): return a list of values
dict.itervalues(): extracting value from dict in each iteration step [retired in python3]
dict.items(): return a list of entities
dict.iteritems(): extracting a pair of key and value from dict in each iteration step [retired in python3]
example
//Code==========
d = { 'Joanna': 100, 'Lisa': 85, 'Bart': 59, 'Paul': 74 }
sum = 0.0
for s in d.itervalues():
sum += s
print sum/len(d)
//Result==========
79.5
Forget about those methods which have prefix of
iter
