# Sequence Utilities

Labrat provides focused Python utilities for nucleotide composition, DNA complements, and FASTA translation. They fit quick checks in scripts, notebooks, and teaching examples.


# Count canonical nucleotides

``` python
from labrat.genetics import atgc_content

counts = atgc_content("ATGCGAT")
print(counts)
```

The result is:

``` text
{'A': 2, 'T': 2, 'G': 2, 'C': 1}
```

Input is case-insensitive. Counts include `A`, `T`, `G`, and `C` only, so the total can be smaller than the submitted sequence length.


# Create a complementary strand

``` python
from labrat.genetics import complementary_dna

complement = complementary_dna("ATGN")
print(complement)
```

The result is `TACX`. Non-canonical characters become `X`. The function returns the direct complement in the submitted order. Reverse this sequence when you need the reverse complement.


# Translate a FASTA sequence

Create a small FASTA file whose nucleotide count is divisible by three:

``` text
>example
ATGAAATGG
```

Translate it with:

``` python
from labrat.genetics import dna2aminoacid

protein = dna2aminoacid("example.fasta")
print(protein)
```

The result is `MKW`. Labrat removes whitespace, accepts lowercase sequence characters, and skips every line beginning with `>`. Stop codons are returned as `_`, and translation continues with the next codon.

Translation raises an error for an empty sequence, a length that leaves a remainder after division by three, or a codon containing a character outside `A`, `T`, `G`, and `C`.


# Laboratory calculations

Labrat also provides laboratory calculations through its Python API. These functions accept plain numeric values, so confirm the intended units before using a result in experimental work.