Let's say I have a string
str1 = "TN 81 NZ 0025"
two = first2(str1)
print(two) # -> TN
How do I get the first two letters of this string? I need the first2 function for this.
7 Answers
It is as simple as string[:2]. A function can be easily written to do it, if you need.
Even this, is as simple as
def first2(s):
return s[:2]
2 Comments
SDsolar
This one is the right way to grab the first two characters. You answered the OP just right, so upvote. However, I would never use a function for this. I prefer to make it explicit in the code without having to chase down functions for verification. As in
firsttwo = somestring[:2] in-line in the main code
ShinTakezou
I agree, in fact I wrote “A function can be easily written to do it, if you need.” It wouldn't make sense to have tons of functions like
first2, first3, first4…In general, you can get the characters of a string from i until j with string[i:j].
string[:2] is shorthand for string[0:2]. This works for lists as well.
Learn about Python's slice notation at the official tutorial
Comments
t = "your string"
Play with the first N characters of a string with
def firstN(s, n=2):
return s[:n]
which is by default equivalent to
t[:2]
Comments
Heres what the simple function would look like:
def firstTwo(string):
return string[:2]
Comments
In python strings are list of characters, but they are not explicitly list type, just list-like (i.e. it can be treated like a list). More formally, they're known as sequence (see http://docs.python.org/2/library/stdtypes.html#sequence-types-str-unicode-list-tuple-bytearray-buffer-xrange):
>>> a = 'foo bar'
>>> isinstance(a, list)
False
>>> isinstance(a, str)
True
Since strings are sequence, you can use slicing to access parts of the list, denoted by list[start_index:end_index] see Explain Python's slice notation . For example:
>>> a = [1,2,3,4]
>>> a[0]
1 # first element, NOT a sequence.
>>> a[0:1]
[1] # a slice from first to second, a list, i.e. a sequence.
>>> a[0:2]
[1, 2]
>>> a[:2]
[1, 2]
>>> x = "foo bar"
>>> x[0:2]
'fo'
>>> x[:2]
'fo'
When undefined, the slice notation takes the starting position as the 0, and end position as len(sequence).
In the olden C days, it's an array of characters, the whole issue of dynamic vs static list sounds like legend now, see Python List vs. Array - when to use?
Comments
All previous examples will raise an exception in case your string is not long enough.
Another approach is to use
'yourstring'.ljust(100)[:100].strip().
This will give you first 100 chars. You might get a shorter string in case your string last chars are spaces.
1 Comment
djvg
Not true: e.g.
''[:2] just returns ''. No exception.For completeness: Instead of using def you could give a name to a lambda function:
first2 = lambda s: s[:2]
1 Comment
wjandrea
Named lambdas are bad practice. Use a
def instead.
str1.split()[0]also works, and may make more sense if you also need the other fields.str1.split()[0]andstr1[0]are two very different pieces of code."".join(str1.split()[:2])is redundant if there is not double spacing andstr[:2]achieves the same.str1.split()[:2]? U2EFI saidstr1.split()[0]