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In this article, the editor introduces in detail "how to define iteration in for cycle in Python". The content is detailed, the steps are clear, and the details are handled properly. I hope that this article "how to define iteration in for cycle in Python" can help you solve your doubts.

For cycle of Python

Python is a collection-based iteration.

For in: # is a collection of objects-- for example, lists or tuples. # body of the loop a = ['Cao Cao', 'print', 'equipment'] for i in a: print (I)

Output:

Cao Cao

Cymbals

Equipment

An iterable object that can be passed to the built-in Python function iter () for processing and returned as an iterator

Iter ('Cao Cao Yaoyi') # Stringiter (['Cao Cao', 'Yueji', 'Jiaoji']) # Listiter (('Cao Cao', 'Yueyi', 'Jieqi') # Tupleiter ({'Cao Cao', 'Yueji'}) # Setiter ({'Cao Cao': 1 "Dict": 2, "equipment": 3}) #

Objects that cannot be iterated

Iter (1) # IntegerTraceback (most recent call last): File ", line 1, in TypeError: 'int' object is not iterableiter (1.1) # FloatTraceback (most recent call last): File", line 1 In TypeError: 'float' object is not iterableiter (len) # Built-in functionTraceback (most recent call last): File ", line 1, in TypeError:' builtin_function_or_method' object is not iterable

An iterator is a value producer that produces continuous values from its associated iterable objects. The built-in function next () is used to get the next value from the iterator.

List_ = ['Cao Cao', 'itr', 'itr'] itr = iter (list_) itrnext (itr), 'Cao Cao' next (itr), 'next (itr)'

Use the built-in list (), tuple (), and set () functions to get all values from the iterator at once.

List_ = ['Cao Cao', 'Jiaoyi', 'Jiaojie'] itr = iter (list_) list (itr) ['Cao Cao', 'Jiaoyi', 'Jiaoqi'] itr = iter (list_) tuple (itr) ('Cao Cao', 'Jiaoyi', 'Jiaoqi') itr = iter (list_) set (itr) {'Jiaogui', 'Cao Cao', 'Jiaoyi'} traversing the dictionary

A dictionary traversal loop in which loop variables are assigned to dictionary keys.

D = {'Cao Cao': 1, 'equipment': 2, 'equipment': 3} for k in d: print (k)

Output:

Cao Cao

Cymbals

Equipment

The operation of accessing dictionary values

For k in d: print (d [k]) # output: # 1#2#3for v in d.values (): print (v) # output: # 1 / 2 / 3

Traverse the keys and values of the dictionary at the same time. The loop variable for is not limited to a single variable, but can be a tuple.

I, j = (1,2) print (I, j) 1 2for I, j in [(1,2), (3,4), (5,6)]: print (I, j)

Output:

1 2

3 4

5 6

The dictionary method items () effectively returns the list of key / value pairs as a tuple.

D = {'Cao Cao': 1, 'weapon': 2, 'equipment': 3} d.items () dict_items ([('Cao Cao', 1), ('bike', 2), ('Jia Jie', 3)]) d = {'Cao Cao': 1, 'Qing': 2,'Qi': 3} for k, v in d.items (): print ('k =', k,', v =', v)

Output:

K = Cao Cao, v = 1

K = recently, v = 2

K = equipment, v = 3

Range () function

Python provides a built-in range () function that returns an iteration that produces a sequence of integers.

Range () returns an iteration that produces an integer that begins with 0, up to but not including the numeric value

X = range (5) xrange (0,5) type (x)

Range objects are iterable, so you can iterate through them through for loops to get values.

For n in x: print (n)

Output:

0

one

two

three

four

List () and tuple () get the values of all the loop traverses at once.

List (x) [0,1,2,3,4] tuple (x) (0,1,2,3,4)

Range (,) returns an iteration result.

List (range (5, 20, 3)) [5, 8, 11, 14, 17] # defaults to 1list (range (5, 10, 1)) [5, 6, 7, 8, 9] list (range (5, 10)) [5, 6, 7, 8, 9] # the numerical range must be list (range (- 5, 5)) [- 5, 4,-3,-2,-1, 0, 1, 2, 3, 4] list (range (5) -5)) [] list (range (5,-5,-1)) [5, 4, 3, 2, 1, 0,-1,-2,-3,-4] break statement and continue statement

Break terminates the loop completely.

For i in ['Cao Cao', 'Fengyi', 'Jijie']: if'in I: break print (I)

Output:

Cao Cao

Continue terminates the current iteration and proceeds to the next iteration.

For i in ['Cao Cao', 'Fengyi', 'Jijie']: if'in I: continue print (I)

Output:

Cao Cao

Equipment

Else statement

The clause else of the for loop is similar to the use of the while loop.

For i in ['Cao Cao', 'Jiaoyi', 'Jijie']: print (I) else: print ('over.')

Output:

Cao Cao

Cymbals

Equipment

End.

Else will not be executed if the list is break by a statement.

For i in ['Cao Cao', 'Jiaoyi', 'Jijie']: if I = = 'thanks': break print (I) else: print ('over.')

Output:

Cao Cao

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