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Introduction to python startswith() method
Python is well known for its various and powerful built-in functions.
One of its functions, which we will cover today is the python
startswith() method. Sometimes, we might need to check the starting
part of any of the strings for the programming purpose. In such a case,
the python startswith() method helps us to do. In this tutorial, we
will learn about startswith() method in detail considering different
examples.
We will also cover the different types of parameters that this method
can take and how they are useful in solving real problems. This
tutorial will help you to get a deep knowledge of the python
startswith() method.
Getting started with python string startswith() method
Before jumping into the python startswith() method, we should know
about the indexing of string in Python, Because later in this tutorial
we will use string indexing to locate and search a piece of string at a
specific location by providing it index number. As we all know, a string
is a sequence of characters such as numbers, spaces, letters and
symbols. We can access different parts of strings in the same way as we
do for lists. Every character in a string has an index number starting
from 0 to so on. The index is simply the location of a character in the
string. For example, here is one string “Bashir”, the character “B” is
at index 0, “a” is at index one, and so on.
Syntax of python string startswith() method
The python startswith() method returns True if a string starts with
another specified string, else it will return False. This method is
very useful when we want to search for a specific piece of string. Here
is a simple syntax of startswith() method.
string_name.startswith(sub_string/tuple, [, start [, end]])
The python string startswith() method accepts the following
parameters:
prefixis a string or a tuple of strings to search for. Theprefixparameter is mandatory.startis the position that the method starts looking for theprefix. Thestartparameter is optional.endis the position in the string that the method stops searching for theprefix. Theendparameter is also optional.
Note that the python startswith() method is case-sensitive.
In other words, it will look for the prefix case-sensitively. For
example if we have a string “Bashir” and if apply the python
startswith() method to find if the string starts with the letter “b”,
we will get False, because treats upper case B as a different
character and lower case b as different.
Examples of Python string startswith() method “without” start parameter
As we already discussed that the python startswith() takes one
required and two optional parameters. In this section, we will take
examples by providing only the required parameter. Let say we have
different sentences and we want to know if ech of the sentences starts
with a specific word or letter. We can do this by using python
startswith() method. See example below:
# string one
string1 = "This is our school"
# string two
string2 = "My name is khan"
# string three
string3 = "+996-3028374"
# check string
print(string1.startswith("This"))
print(string2.startswith("my"))
print(string3.startswith("+996"))
Output:
True
False
True
Notice that we get False for the string “my” as well because there
is a difference between uppercase letters and lowercase letters. If we
want our program to ignore the case differences and make it
case-insensitive, we can do that by applying the following different
methods.
# string
string = "My name is khan"
# checking
print(string.lower().startswith("my"))
Output:
True
Notice that this time we get True and our program ignored the case
difference. Actually, it didn’t ignore it, we applied lower() method
on our string which converts all the letters of the main string into
lower case and then checks the given string. If our input string is in
upper case then we have to convert our main string into uppercase as
well. See the code below:
# string
string = "My name is khan"
# checking
print(string.upper().startswith("MY"))
Output:
True
This time we used upper() method to convert our main string into the
upper case to ignore the case difference.
Examples of Python string startswith() method “with” start parameter
Now let us solve some examples by giving an optional parameter of
starting string. It is actually giving an index number so that the
python startswith() method will start looking for the prefix from the
specified position. See the example below which takes an optional
parameter.
# string 1
string1 = "My name is khan"
# string two
string2 = "this is my school"
# string three
string3 = "+996-34343435"
# checking
print(string1.startswith("name", 3))
print(string2.startswith("school", 11))
print(string3.startswith("+996", 3))
Output:
True
True
False
Notice that we get True for the first two cases because the specified
position of the given string matches while we get False in the last
case because the specified string is not found in the given position.
As we did previously, we can ignore the case sensitivity by using
lower() and upper() methods. See the example below:
# string 1
string1 = "My name is Khan"
# checking
print(string1.startswith("khan", 11))
# ignores the case difference
print(string1.lower().startswith("khan", 11))
Output:
False
True
Notice that we get False in the first case because we didn’t apply
lower() method and it gives False because of case difference. While
in the second one, we applied lower() method so that it first converts
the main string into lower case and then checks for the given
sub-string.
In the same way, we can ignore the case difference by applying upper()
method, if our input string is in upper case letters. See the example
below:
# string 1
string1 = "My name is Khan"
# checking
print(string1.startswith("KHAN", 11))
# ignores the case difference
print(string1.upper().startswith("KHAN", 11))
Output:
False
True
Notice that we get True for the case where we applied upper() method.
Examples of python startswith() method with ending parameter
So far we have learned how to use python startswith() method and how
the starting parameter works. In this section, we will learn about the
python startswith() method by giving one more optional parameter and
we will see how it works. The second optional parameter that this method
takes is the ending position of the sub-string. See the following
example to get yourself familiar with the ending parameter in
startswith() method.
# string 1
string1 = "My name is Khan"
# string two
string2 = "this is my school"
# string three
string3 = "+996-3746383"
# checking
print(string1.startswith("name", 3, 11))
print(string2.startswith("is", 3, 14))
print(string3.startswith("+9", 0, 12))
Output:
True
False
True
Notice that we get True for the first and last one and get False for
the second one. Python startswith() method will take the two optional
parameters and checks the availability of sub-strings in the specified
potions ( starting and ending).
We can also apply the lower() and upper() method to ignore the case
differences. See the example below:
# string 1
string1 = "My name is Khan"
# checking
print(string1.startswith("Name", 3, 11))
print(string1.upper().startswith("NAME", 3, 11))
print(string1.lower().startswith("name", 3, 11))
Output:
False
True
True
Notice that we get False in the first one because python
startswith() method is case sensitive.
Use python startswith() method with tuple
So far we have learned how we can apply the python startswith() method
on strings by taking different examples. Now in this section, we will
see how we can use a tuple to search a sub-string. This method is useful
when we want to know if any of the multiple string is present in our
main string or not. See the example below which takes a
tuple of
strings and searches using python startswith() method.
# string 1
string1 = "My name is Khan"
# string two
string2 = "this is my school"
# checking using tuple
print(string1.startswith(("My", "this", "We")))
print(string2.startswith(("We","they", "This")))
Output:
True
False
Here the python startswith() methods, will take each element from the
tuple and searches in the given string, if the substring is found, it
will return True, else will return False. In the above example
notice that it returns True for the first case because the sub-string
“My” was in our main string while it returns False for the second case
because non of the sub-strings were found in our main string.
We can also use lower() and upper() methods to ignore the case
differences and can also use the optional two parameters ( starting and
ending) with tuple as well. See the following example.
# string 1
string1 = "My name is Khan"
# string two
string2 = "this is my school"
# checking using tuple
print(string1.startswith(("My", "this", "We"), 0, 10))
print(string2.upper().startswith(("We","they", "THIS"), 0, 10))
Output:
True
True
Summary
The Python startswith() method returns True if the string starts
with the specified value, otherwise False. This method is very useful
we need to search for a substring in a text. It can also take an
optional two parameters to specify the starting and ending positions of
the substring. If we will not specify the starting position of the
substring, then by default, it will check at index 0. In this
tutorial, we learned about python startswith() method by taking
different examples. We discussed about the optional parameters and
learned how they actually work. Moreover, we also learned how to give a
tuple of strings to search in a text. All in all, this tutorial covers
everything about python startswith() method.
