Generally, a 'for'
loop is used to repeat a code N number of times, where N is the number of items in the sequence or collection. In Python, we can use for loop to iterate over a list, a tuple, a dictionary, a set, or a string.
chars = ["a", "b", "c"]
for c in chars:
print(c)
1. Syntax
The syntax to use a for loop is:
for val in sequence:
statement(s)
Here, the variable val
represents a value from the sequence, for the current iteration. After each iteration. the value points to the next available value in the sequence. Once all the values have been iterated, the for
loop terminates.
2. Python for
Loop Examples
2.1. Looping through a List
Python program to iterate over a list of items using for
loop. This program prints all the names stored in the list.
names = ["alex", "brian", "charles"]
for x in names:
print(x)
2.2. Looping through a String
In Python, strings are iterable. They are a sequence of characters, so we can iterate over the characters as follows:
name = "alex"
for x in name:
print(x)
2.3. Looping through a Dictionary
A dictionary is a collection data type and we can iterate over its key-value pairs as follows:
colors_dict = {'color': 'blue', 'fruit': 'apple', 'pet': 'dog'}
for key in colors_dict.keys():
print(key)
for item in colors_dict.items():
print(item)
3. The break
and continue
Statements
The break
statement is used to stop the iteration and exit the for
loop, when a certain condition is met:
names = ["alex", "brian", "charles"]
print("Loop started")
for x in names:
print(x)
if x == "brian":
break;
print("Loop ended")
The continue
statement is used to stop the current iteration and jump to the next iteration in the loop. It does not terminate the for
loop.
names = ["alex", "brian", "charles"]
print("Loop started")
for x in names:
if x == "brian":
continue;
print(x)
print("Loop ended")
4. The else
Statement
The for
loop can have an optional else
block as well. It is called for...else
statement.
names = ["alex", "brian", "charles"]
for x in names:
print(x)
else:
print("No name is left in the list")
5. Looping within range()
In Python, the for
loop can be used with range()
function as well. The range()
generates a sequence of values starting with 0 by default. For example, range(10)
will generate numbers from 0 to 9 (10 numbers).
for i in range(5):
print(i)
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